To determine to what extent plant growth and morphology are sensitive to perturbed carbon metabolism, we grew Arabidopsis thaliana L. (Heynh.) seedlings for 10 d in the presence of various carbon compounds and measured the length and diameter of the primary root. Compounds fell into three groups based on their effect on root length: group one supported about as much elongation as sucrose; group two supported about the same elongation as occurred in the absence of sugar; and group three reduced or even eliminated root growth. No compound changed the diameter of the root notably, although there was a weak, positive correlation between root diameter and elongation. To investigate the inhibition of root elongation by mannose, we transplanted seedlings on to test media and measured primary root growth over the subsequent 2 d. Mannose scarcely changed root diameter, in contrast to 2-deoxyglucose, which caused marked swelling, similar in extent to that caused by tunicamycin. Mannose inhibited elongation rate by 90% within 24 h and required a further 2 d to reduce the elongation rate to zero, with the saturating dose being 30 mM in the presence of 3% sucrose and 0.3 mM in its absence. By contrast, cell production rate was little affected over the first 2 d of treatment. The inhibition of elongation by mannose was not reproduced by two sugar analogs that cannot be phosphorylated on carbon six, was not affected by manipulating phosphate levels in the medium, and was largely prevented by simultaneous treatment with either 30 mM mannoheptulose, 1 mM glucose, or 56 mM fructose. These results suggest that mannose inhibits root elongation via hexokinase-mediated sugar signaling.
The effects of the deprivation of boron (B) on Rhizobium–legume signaling and preinfection events have been investigated in pea (Pisum sativum L. cv. Argona). The capacity of root exudates to induce the activity of nodulation genes was modulated by B nutrition in the host plant. Exudates derived from B-deficient pea plants led to a low level of nod-gene expression that could be correlated with poor root hair curling. However, inoculation of B-deficient plants with bacteria grown in the presence of the nod-gene inducing hesperetin, restored root hair curling. The attachment of bacteria to roots was also diminished in plants grown in the absence of the micronutrient, and it was not recovered by hesperetin. Both phenomena provoked a reduction in nodulation of more than 50%. Furthermore, infection thread development was arrested at very early stages, and cell invasion by endocytosis was precluded, leading to almost empty of bacteria B-deficient nodules.
It has been indicated that salinity inhibits maize (Zea mays L.) leaf growth and leaf cell expansion by increasing the apparent yield threshold of the cell wall. We tested whether this increase in the apparent yield threshold was a physical property of cell walls, using in vitro creep-type assays. Salinity had no significant effects on cell wall structural properties based upon several different in vitro assays. In support of these results, there were no differences between control and salt-stressed plants in their total apoplastic concentration of cell wall proteins, in the activity of apoplastic peroxidases or xyloglucan endotransglycosylase. We conclude that short-term salinity does not appear to inhibit maize leaf elongation by hardening the physical structure of the cell walls of the growing zone.
Epiphytes experience frequent and rapid changes in water availability andlight intensity. The role of carotenoids and tocopherols in photoprotection ofseven fern species (Asplenium cuspidatum Lam.,Phlebodium areolatum (HB ex Willd.) Smith,Polypodium puberulum Schl. & Cham.,Po. plebeium Schl. & Cham.,Elaphoglossum glaucum Moode,E. petiolatum (Sw.) Urb., andPleopeltis mexicana (Fée) Mickel & Beitel)with different adaptations against drought were investigated. The plants weresampled dark adapted (treatment I), and after light exposure with thesubstrate present (treatment II), with the substrate removed (treatment III)and with substrate and rhizomes removed (treatment IV) to induce increasing degrees of drought stress. The degree of dehydration reached does not resultin permanent damage and was also observed in the field. While none of thetreatments induced significant chlorophyll (chl) degradation, all plantsshowed strong de-epoxidation of the xanthophyll cycle on light exposure (up toa de-epoxidation state of 70%), but without an additional effect ofdesiccation. Most species showed a rapid increase (within hours) ofcarotenoids (mainly β-carotene and lutein) and α-tocopherol onexposure. In A. cuspidatum, a species with no apparentadaptations to drought, drought stress in combination with light resulted inan increase of tocopherols from 35 nmol mol–1 chl(treatment I) to 400 nmol (treatment IV). This effect was not significant inthe drought-deciduous species with succulent rhizomes,Po. puberulum (about 10 nmolmol–1 chl) and Ph. areolatum(5 to maximum 40 nmol), which experience little desiccation under fieldconditions. This short-term induction of tocopherols and carotenoids has notbeen reported for other plants under light stress and is probably related tothe epiphytic life form.
The Granier sap flow measuring system that normally uses one analogue input channel of a datalogger for each sensor was modified to enable one channel to measure the average value of signals from two or more sensors. The sap flux density calculated from this average value of signals was very close (difference < 6.0%) to the arithmetic mean of the sap flux densities measured separately by means of individual sensors (using two or more input channels). The dynamics of the sap flux density measured by the modified method were similar to those measured by the original method. On a per-channel basis, the modified method reduced the ‘estimation error’ of sap flux density by 4–14-fold compared to the original method. By using the modified Granier system, the error in sap flow measurement that is usually associated with limited sampling can be substantially reduced without the need for extra dataloggers, the greatest item of expense.
In previous studies with tomato (Lycopersicon esculentum L.) exposed to a low level (3.7 kJ m –2) of UV-C (λ: 254 nm) radiation, which is defined as a beneficial level, we report a delay in fruit ripening by at least 1 week for treated fruit. In the present study, we investigate the changes in the activities of different enzymes involved in defense mechanisms, such as guaiacol peroxidase, ascorbate peroxidase, catalase, superoxide dismutase, ascorbate oxidase, lipoxygenase and phenylalanine ammonia lyase in tomato fruit in response to a beneficial level of UV-C. The irradiation leads to an increase in the guaiacol peroxidase and ascorbate peroxidase activities, whereas catalase activity remains similar to the control. The activities of superoxide dismutase and ascorbate oxidase were significantly reduced after UV-C exposure. In UV-C-treated fruit, an increase of lipoxygenase and phenylalanine ammonia lyase activities occurred within the first 5 d, followed by a second period in which these activities were below those of the control. Our study suggests that the level of UV-C used induced a rapid but moderate accumulation of photooxidation products, to which plants react by stimulating their defence mechanisms against oxidation. This activation may explain the delay observed in ripening and senescence of irradiated tomato fruit.
To analyse the contribution of dormancy and dehydration tolerance to drought survival of perennial grasses, we compared Poa bulbosa L., which is classified as a resurrection plant, with one of the most drought resistant cultivars of Mediterranean Dactylis glomerata L. Comparing periods when dormancy was induced in Poa (summer) and not induced (winter), we aimed to ascertain the presence of differential plant responses between dormancy and dehydration tolerance and to characterise water status, sugar and dehydrin accumulation in surviving organs of Poa and Dactylis, in relation to their ability to survive intense drought. Irrespective of the dormancy status of Poa, the bulbs of this species had a final water content lower than 10% and survived an extreme drought. This could be associated with the accumulation of sucrose and the expression of a high number (>10) of dehydrins that peaked when the water content of the bulbs fell below 50%, whether this dehydration was due to dormancy induction or increasing soil water deficit. The independence of dormancy to dehydration tolerance was reinforced by the expression of a specific dehydrin (approx. 28 kDa) found only in irrigated, but dormant, tissues of Poa. The Dactylis exhibited contrasting survival between experiments (46 and 0% after a summer and winter drought, respectively). The mortality was associated with a significantly higher rate of decrease of the membrane stability of leaf bases of Dactylis in winter and with barely detectable amounts of sucrose contents in droughted roots. However, neither the water-soluble carbohydrate concentration in leaf bases nor the overall accumulation of dehydrins could be related to the contrasting survival of this Dactylis between the two seasons. Since in seeds of Poa and Dactylis, the accumulation of dehydrins was comparable with that found in droughted aerial tissues of the same species, the expression of these proteins must interact with other mechanisms to confer dehydration tolerance.
Conditions for Agrobacterium-mediated transformation of wheat (Triticum aestivum L.) were defined using wheat suspension cells as a model system and green fluorescent protein (GFP) as a visual marker. Different strains of Agrobacterium tumefaciens were compared using established wheat cell suspension cultures, where the frequency of cell clusters showing transient activity of GFP ranged from 2 to 52%. High levels of transient GFP activity and stable transformed callus lines were obtained with plasmid pTO134 containing a gfp gene with an enhanced CaMV 35S promoter and a bar gene with a 35S promoter in combination with Agrobacterium strain AGL0. These results suggest that the important variables in Agrobacterium-mediated transformation of wheat cells include media composition, Agrobacterium strain, plasmid vector and the addition of virulence-inducing agents such as acetosyringone. The conditions deemed optimal for transformation of wheat suspension cell lines were applied to scutella isolated from immature embryos and scutella-derived calli. Transient GFP expression in these tissues ranged from 10 to 75% and, while quite variable among and within cultivars, stably transformed scutellum-derived callus was obtained. Further studies with scutellum-derived calli suggested that variables such as duration of pre-inoculation culture and co-cultivation, as well as co-cultivation temperature, were also important. Optimisation of these variables resulted in the recovery of transformed wheat plants at a transformation frequency of 1.8%, which is comparable with other reports.
In view of the essential role of oxidative process in the development of pathogen resistance in plants, the aim of the present study was to determine the individual effect of a fungicide, as well as to determine the combined effect of the fungicide and boron (B) on superoxide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), and ascorbate peroxidase (APX) activities and H 2 O 2 levels in tobacco plants (Nicotiana tabacum L. cv. Tennessee 86). The fungicide applied was carbendazim (carb) at a concentration of 2.6 mM . Boron was applied as H 3 BO 3 at: 1.6 mM (B1), 4 mM (B2), 8 mM (B3), 16 mM (B4), 32 mM (B5), and 64 mM (B6). The results indicated that foliar application of carbendazim by itself does not increase SOD, GPX, CAT or APX activities or H2 O2 foliar accumulation. The combined application of carbendazim and B increased SOD, GPX, CAT, and APX activities, especially in carb-B3 and carb-B4 . This effect may signify an additional tolerance mechanism to pathogenic infection, given the participation of these enzymes in the early phases of the plant–pathogen interactions.
Grapevines are considered well adapted to high irradiance during growth. It is still controversial, however, whether photoinactivation of photosystem II is completely avoided in high light-acclimated grapevines growing in the field. This study examines the functional stability of PSII in leaf discs (floated on water) of field-grown, high light-acclimated grapevines as a function of photon exposure. Measuring functional PSII units by flash-induced oxygen evolution, it was found that the susceptibility of PSII to photoinactivation was less in sun-exposed leaves than shade leaves of Vitis riparia Michaux, and enhanced by lincomycin, an inhibitor of chloroplast-encoded protein synthesis. Vitis vinifera L. cv. Chardonnay, grown in a glasshouse with slightly lower irradiance, exhibited an intermediate susceptibility. Significantly, the dark-relaxed quantum efficiency of PSII, measured as (Fm – Fo)/Fm, where Fm and Fo are the chlorophyll (Chl) fluorescence yields for closed and open reaction centres, respectively, declined much more slowly than did the number of functional PSII units in V. riparia. Thus, measurements of (Fm – Fo)/Fm may give an impression of little photoinactivation of PSII, even when nearly half of functional PSII units may be lost. By contrast, the parameter 1/Fo – 1/Fm is a more linear indicator of functional PSII units. The results indicate that grapevines may suffer photoinactivation of PSII, at least when leaf discs are floated on water.
This study investigated the chloroplast pigment content of the Australian mistletoe Amyema miquelii (Lehm. ex Miq.) Tiegh. over diurnal periods in sun- and shade-acclimated leaves. Amyema miquelii exhibited the typical higher plant complement of neoxanthin, the xanthophyll cycle pigments, lutein, chlorophylls a and b and β carotene. Substantial levels of lutein epoxide were also present. Interestingly, diurnal light exposure elicited a decrease in lutein epoxide that paralleled the decrease in violaxanthin. Compared with shade-acclimated leaves, sun leaves exhibited reduced lutein epoxide and violaxanthin levels and higher chlorophyll a/b ratios. It is clear that the pools of violaxanthin and lutein epoxide respond in parallel to both diurnal light changes and sun–shade acclimation, although there seemed to be some differences in the recovery characteristics. These results raise a question as to whether lutein and lutein epoxide cycling may provide an auxiliary means of energy dissipation for some species.
Arabidopsis thaliana L. has many features favoring its use as a model in studies of plant-growth-promoting rhizobacteria (PGPR), such as diazotrophs. Several niches are colonized in the root system of Arabidopsis, including xylem, and intact colonized roots can be observed microscopically without sectioning of tissues. Studies of plant genes involved in colonization are facilitated by the ease with which plants are transformed and by the availability of mutant lines and other accessions obtainable from stock centers. Lines of Arabidopsis carrying reporter gene fusions are helping to reveal the pattern of expression of previously cloned plant genes induced by rhizobacteria. Studies utilizing indole-3-acetic acid (IAA)-producing PGPR and Arabidopsis that contain an auxin-responsive GUS fusion suggest that plants perceive IAA released by bacteria in the rhizosphere. The role of flavonoids in the colonization of non-legumes is being assessed using transgenic Arabidopsis with altered flavonoid metabolism and using tt mutants, which lack functional versions of specific genes for flavonoid metabolism. Studies of plant defence and of stress responses are producing molecular data on plant genes induced by inoculation of Arabidopsis roots with non-pathogens.
This paper summarizes a multinational collaborative project to search for natural, intimate associations between rhizobia and rice (Oryza sativa L.), assess their impact on plant growth, and exploit those combinations that can enhance grain yield with less dependence on inputs of nitrogen (N) fertilizer. Diverse, indigenous populations of Rhizobium leguminosarum bv. trifolii (the clover root-nodule endosymbiont) intimately colonize rice roots in the Egyptian Nile delta where this cereal has been rotated successfully with berseem clover (Trifolium alexandrinum L.) since antiquity. Laboratory and greenhouse studies have shown with certain rhizobial strain-rice variety combinations that the association promotes root and shoot growth thereby significantly improving seedling vigour that carries over to significant increases in grain yield at maturity. Three field inoculation trials in the Nile delta indicated that a few strain-variety combinations significantly increased rice grain yield, agronomic fertilizer N-use efficiency and harvest index. The benefits of this association leading to greater production of vegetative and reproductive biomass more likely involve rhizobial modulation of the plant's root architecture for more efficient acquisition of certain soil nutrients [e.g. N, phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), zinc (Zn), sodium (Na) and molybdenum (Mo)] rather than biological N(2) fixation. Inoculation increased total protein quantity per hectare in field-grown grain, thereby increasing its nutritional value without altering the ratios of nutritionally important proteins. Studies using a selected rhizobial strain (E11) indicated that it produced auxin (indoleacetic acid) and gibberellin [tentatively identified as gibberellin (GA(7))] phytohormones representing two major classes of plant growth regulators. Axenically collected rice root exudate significantly enhanced E11's production of this auxin. This strain extensively colonized the rice root surface under gnotobiotic culture conditions, producing distributions of spatial patchiness that would favour their localized erosion of the epidermal surface, colonization of small crevices at epidermal junctions as a possible portal to enter into the root, and quorum sensing of diffusible signal molecules indicating that their nearest bacterial neighbours are in close proximity in situ. Studies of selected rhizobial endophytes of rice indicated that they produced cell-bound cellulase and polygalacturonase enzymes that can hydrolyze glycosidic bonds in plant cell walls, and non-trifolitoxin bacteriocin(s) that can inhibit other strains of clover rhizobia. Strain E11 was able to endophytically colonize rice roots of varieties commonly used by Filipino peasant farmers, and also to stimulate genotype-specific growth-promotion of corn (Zea mays, maize) under field conditions. An amalgam of these results indicate some rhizobia have evolved an additional ecological niche enabling them to form a three-component life cycle including a free-living heterotrophic phase in soil, a N(2)-fixing endosymbiont phase within legume root nodules, and a beneficial growth-promoting endocolonizer phase within cereal roots in the same crop rotation. Our results further indicate the potential opportunity to exploit this newly described, plant-rhizobia association by developing biofertilizer inoculants that may assist low-income farmers in increasing cereal production (especially rice) with less fertilizer N inputs, fully consistent with both sustainable agriculture and environmental safety.
Effects of low concentrations of HgCl2 on water transport in excised maize (Zea mays L.) roots have been monitored using a reliable system that permits continuous measurement of xylem flux variations. The sap flow of exuding roots treated with 11 M HgCl2 decreased by 80–90% in 10 min at 25˚C. Reversal of this inhibition was obtained using a sulfhydryl [β-mercaptoethanol (β-ME)], or non-sulfhydryl [ethylenediaminetetraacetate disodium salt (EDTA) and ferricyanide (FeCy)] reagents. The time course of reversal was not the same in the three cases. β-ME reversed quickly but not sustainably, whereas EDTA or FeCy reversed slowly and sustainably. Using a cell pressure probe, turgor was measured in the epidermis, and the first layer of cells in the cortex. Turgor was considerably decreased in root epidermal cells after HgCl2 treatment, suggesting that a normal root water-transfer required an optimal turgor in these cells. Recovery of cell turgor, was obtained satisfactorily with FeCy. In parallel with flux measurements, histochemical analyses revealed a localization of Hg only in peripheral root cells, suggesting that Hg targets are localized in the first root cell layers. Involvement of water channels and/or ion transport in the regulation of root water transport is discussed in the light of our data.
Net photosynthesis, individual carbohydrate concentrations, and the activities of some enzymes involved in carbohydrate biosynthesis were monitored in mature apple leaves at regular intervals throughout a natural day/night cycle. Sorbitol was the major carbohydrate in mature apple leaves. Its concentration increased gradually after dawn and reached its highest level of 18.0 mg g –1 fresh weight, and then declined to its lowest level of 9.6 mg g–1 at the end of the dark period. Starch also showed a similar diurnal pattern with a lower maximum of 4.6 mg g –1 fresh weight and a minimum of 1.8 mg g –1 fresh weight. Aldose-6-phosphate reductase (A6PR) activity showed significant diurnal fluctuations, whereas sucrose-phosphate synthase (SPS) activity, under both saturating and limiting substrate conditions, showed no variations. The highest A6PR activity under natural light conditions appeared at 1000 h with 37.2 µmol h –1 g ––1fresh weight, which was about 30% higher than that in the night. The diurnal alteration of A6PR activity was also found under controlled environmental conditions in growth chambers. Treatments of 14/10 h light/dark photoperiod, continuous light and continuous darkness, did not change the pattern of diurnal variation in A6PR activity. Significant correlation between A6PR activity, sorbitol concentration and photosynthetic rate suggested that the processes of photosynthesis and carbohydrate biosynthesis are coordinated.
Abscisic acid accumulation and oxidative stress are two common responses of plants to environmental stresses. However, little is known about their relationships. The purpose of this article is to investigate the effects of reactive oxygen species and nitric oxide on the plant hormone abscisic acid synthesis in root tips of wheat (Triticum aestivum L.) seedlings under drought stress. Detached root tips were subjected to drought stress by naturally evaporating until 20% of their fresh weights were lost. The activities of superoxide synthases and nitric oxide synthase (EC 1.14.13.39) increased after 20 min of treatment and abscisic acid began to accumulate 60 min later. The induction of abscisic acid by drought was strongly blocked by pretreating the root tips with reactive oxygen species eliminators tiron or ascorbate acid, and with nitric oxide synthase inhibitor Nω-nitro-L-arginine or nitric oxide eliminator 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide. Consistent with these results, reactive oxygen species generators diethyldithiocarbamic acid, xanthine–xanthine oxidase and triazole or nitric oxide donor sodium nitroprusside can also induce abscisic acid accumulation in root tips of wheat seedlings. While potentiated by reactive oxygen species, the effect of sodium nitroprusside on abscisic acid accumulation was blocked by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide. Based on these results, we suggest that reactive oxygen species and nitric oxide play important roles in drought-induced abscisic acid synthesis in plant, they may be the signals through which the plant can ‘sense’ the drought condition.
Inorganic phosphate (Pi) uptake systems across the plasma membrane of plant cells have been extensively investigated. Physiological studies have established that Pi is transported into plant cells via co-transport with H+ , and in some plants with Na + , using the driving force provided by the electrogenic H + pump in the plasma membrane. Molecular studies have identified many genes for Pi transporters and are providing insights into the mechanisms of genetic control of Pi transport. There still remain, however, questions as to how Pi uptake systems are regulated at the physiological level. We have found that Pi uptake induces cytoplasmic acidification, and, conversely, that inducing cytoplasmic acidification causes the cytoplasmic Pi concentration to decrease. Both of these responses affect the operation of the H + -pump. These phenomena are discussed in relation to a possible mechanism for the physiological control of Pi uptake by plant cells.
In birch roots (Betula pendula Roth), two members of the Bet v 1 gene family which encode PR 10 proteins have previously been characterized. One of these members, named Bet v 1-sc1, is significantly induced in response to biotic or abiotic factors. We have analysed the expression of Bet v 1-sc1 in birch roots treated either with 1 M indole-3-acetic acid (IAA) or 1 M kinetin using reverse transcription–polymerase chain reaction (RT–PCR), northern blotting and competitive PCR. High accumulation of the Bet v 1-sc1 transcripts was recorded only after auxin application, while kinetin had no effect. By in situ hybridization, we have investigated the localization of Bet v 1-sc1 mRNA in birch roots after induction of the gene by root treatment with 1 M IAA. Using root tip sections, we showed that Bet v 1-sc1 is significantly expressed in the apical meristem and the procambium. In sections taken in the zone producing lateral roots, the presence of Bet v 1-sc1 was found at sites of emerging secondary root primordia. This first report of localization of Bet v 1-sc1 expression suggests that this gene could be involved in the processes leading to lateral root initiation.
Coleoptile length in wheat (Triticum aestivum L.) can be affected by several factors, including genotype, height-reducing genes and environmental factors, including temperature. There is little information on how these factors influence rate and duration of coleoptile growth to determine final coleoptile length in wheat. Coleoptile growth was determined for eight genotypes representing four different height-reducing genes: gibberellic acid (GA)-sensitive, standard height (rht), GA-sensitive semidwarfs (Rht8); and GA-insensitive, semidwarfs (Rht2). These were grown in the dark at three temperatures (12, 16 and 20˚C) and coleoptile lengths measured every 12˚Cd. Logistic growth curves were fitted to coleoptile growth data for each genotype with thermal time as the explanatory variable. Differences in final coleoptile length were largely attributable to differences in rate of coleoptile elongation although there were small differences in duration of growth between genotypes. The longer coleoptile of the rht wheats was achieved through the fastest rate of coleoptile elongation. Coleoptiles of Rht8 wheats were equivalent in final length to rht wheats at 107 mm, but achieved this through a slower growth rate (2.10 mm ˚Cd–1) combined with an increased duration of growth (57˚Cd). In contrast, the shorter coleoptiles of Rht2 wheats resulted from 25% slower rates of elongation than either Rht8 or rht. There were no interactions between the components of coleoptile growth and temperature, although a longer duration and a fast rate of growth combined to increase coleoptile length at 12˚C compared with either 16 or 20˚C. In a second experiment, dry matter partitioning and length of coleoptile, subcrown internode (SCI), shoot and roots were determined after 200˚Cd. In Rht2, the SCI and shoot were short while roots were longer than either Rht8 or rht. Reduced dry matter (DM) partitioning to the coleoptile and SCI and DM retention in the seed reduced the endosperm-use efficiency (EUE) of Rht compared with rht. EUE was poor also in Rht8, apparently through increased respiratory losses. Reduced partitioning of dry matter to coleoptiles and the SCI in Rht2 increased the root : shoot ratio compared with rht or Rht8. We conclude that either increased rate or duration of coleoptile growth could be targeted in a breeding program that aims to increase coleoptile length in wheat.
The accumulation of polymeric proteins and the changes in molecular size distribution of these proteins were followed during grain filling and/or premature desiccation. The accumulation behavior of polymeric proteins and their constituent polypeptides (high and low molecular weight glutenin subunits, HMW-GS and LMW-GS) was determined by reversed phase-high performance liquid chromatography using a NaI/propanol purification procedure. With this new extraction and separation procedure, we have demonstrated that there was a coordinated initiation of storage protein biosynthesis, even if the accumulation rate varied greatly between the two main classes of proteins (i.e. monomeric and polymeric fractions). Moreover, the glutenin subunit composition was largely modified during glutenin accumulation. Both the HMW-GS/LMW-GS and HMW-GS-x/HMW-GS-y ratios increased significantly during the whole cell enlargement phase (from 16 to 37 d after anthesis). By applying premature grain desiccation during this physiological phase, we demonstrated that the polymerization index (SDS-insoluble polymers/total polymers) of the glutenin polymers was closely related to the HMW-GS/LMW-GS ratio of these proteins. An increase in the relative proportion of HMW-GS in glutenins caused the proportion of SDS-insoluble polymers to rise during grain desiccation. From these studies, it appears that the modification of the desiccation rate (grain desiccation at a constant temperature with variable relative humidity levels) induced a parallel modification of the glutenin insolubilization rate but did not affect the polymerization index of the glutenins at maturity.
