The progressive secondary salinisation of irrigated farmland, mostly caused by accumulation in the soil of toxic ions dissolved in the irrigation water and accelerated by climate change, is a major contributor to declining crop yields. The best approach to address this problem should be the genetic improvement of crop salt tolerance, which requires a deep understanding of the underlying molecular mechanisms of tolerance. Over the last two decades, halophytes, plants adapted to natural saline environments, have emerged as ideal models to elucidate these mechanisms. In this chapter, we summarise some examples of studies conducted on a wide variety of halophytes, which provide valuable insights into stress tolerance mechanisms, from anatomical adaptations and physiological and biochemical responses to molecular approaches, including gene isolation and characterisation and "omics" technologies. Furthermore, the effects of climate change on natural saline habitats are also mentioned, highlighting concerns about biodiversity loss, local extinction of sensitive species, and the proliferation of invasive species under evolving climatic conditions. Knowledge of tolerance levels and mechanisms becomes essential for designing and implementing effective conservation and regeneration programmes. The final section includes a more personal view on halophyte research, based on our group's work over the last 20 years, with some comments and recommendations to pursue work with this amazing group of salt-tolerant plants.
In this paper, the Papaveraceae family is analyzed from the perspective of molecular phylogeny and pollen ultrastructure carried out by our research group and new data is added until all its subfamilies and tribes are completed. The work focuses on all ontogenetic aspects of the ultrastructure of the wall and pollen aperture, its nutritional tissue, and also the presence of multilamellar cytoplasmic bodies, both in the pollen grain and in the pollen tube, also highlighting the importance of the genes involved in the formation and development of apertures. To the three models previously described by us, a new variant is added for some species of Meconopsis, and the granular infratectum is also considered a derived character and not primitive as previously. The lamellar foot layer is a character present in Euptelea and in most species of the Fumarioideae subfamily. This data is corroborated by cytochemical techniques. Regarding the three models of aperture development already described, we added a new model in Bocconia and Macleaya with endoaperture and two new variants with exine oncus and/or intine oncus. Another feature studied is the tapetum which is of the secretory type and it presents ultrastructural differences between orbicules-producing and non-orbicules-producing species. In relation to the multilamellar bodies found in the cytoplasm near the apertures and at the apex of the growing pollen tube, we have related these structures, which are accumulations of membranes, as a reserve of membranes to be used at times of maximum growth. Finally, we have been able to verify that the INP1 gene involved in the development of apertures is present in basal eudicots (EcINP1). Furthermore, in the samples of inaperturate pollen obtained, it has been found that the apertures do not seem to be essential for the germination of pollen grains in the species studied. We believe that ultrastructural and genetic studies should continue in as many species of the order Ranunculales as possible, which would add value to the characters found in Papaveraceae and would also serve as a model for other groups of angiosperms.
Development of plants and animals depends on the formation of complex vascular systems for the delivery of water, nutrients, and hormonal signals. This review clarifies major controlling mechanisms that regulate vascular differentiation, regeneration, adaptation, and evolution of plants, which were discovered during the past 50 years. Hypotheses and evidence on the hormonal mechanisms that regulate vascular differentiation are discussed, focusing on phloem and xylem relationships, control of vessel width, fiber differentiation, leaf and flower development, root initiation, evolution of ring-porous wood, parasitism, gall formation, cancer development and prevention.
This review gives an account of one agronomists’ and his teams’ contribution to the understanding of some aspects of the physiology and ecology of grassland plants and ecosystems. The topics span across multiple spatial and temporal scales, from the cellular basis of leaf growth in grasses, to functional components of CO2 exchange at leaf to ecosystem scale, the role of carbohydrate (fructan) stores in recycling of sucrose and supporting respiration and vegetative and reproductive growth in benign and stressful conditions, the multi-seasonal 18O-ecohydrology of a pasture, last-century climate change effects on intrinsic water-use efficiency and canopy-integrated stomatal conductance of a range of grassland communities with contrasting nutrient status and plant functional group composition, regional scale changes of the C4/C3 abundance ratio in Inner Mongolia grassland, to ecological fingerprints of cattle based agroecosystems derived from the stable isotope composition of animal tissues, such as hair and milk. Much of the research relied on the development or improvement of methodology, including stable isotope techniques, encompassing 13CO2/12CO2 gas exchange and dynamic (or steady-state) labelling systems from leaf-scale in controlled conditions to ecosystem-scale in natural environments, analysis of tracer kinetics with compartmental models, and interpretations of natural isotope signals in biomass (13C/12C, 15N/14N, 18O/16O) or water pools (18O/16O, 2H/1H) of soil, vegetation, and animals.
Noncoding RNA molecules with gene expression regulatory roles have been intensively studied over the last decade across all groups of organisms. The small RNAs, usually ranging between 20 and 24 nucleotides in length, are among major regulators of diverse biological processes in plants, from growth and development to environmental responses. In forest trees, these molecules have also been identified and in some cases shown to play important functions in the control of the characteristic features of these organisms. Despite the difficulties in the investigation of small RNAs in forest trees due to the lack of wide genome resources and the usually challenging experimental characterization, several studies are already available in forest species from the angiosperms and gymnosperms. Such studies will be reviewed here, focusing on the microRNAs associated with embryo/seed development, phase change, flowering, secondary growth, and responses to abiotic stresses and biotic interactions.
CaCO3 precipitates occur inside a few cyanobacteria and green algae. More common is precipitation on the surface of cyanobacteria, a range of algae and aquatic plants, and in invaginations of the cell wall in terrestrial plants (cystoliths). In coccolithophores and calcified dinoflagellates, CaCO3 is precipitated with organic matter in intracellular vesicles and the resulting structures are externalised. The precipitation of CaCO3 on the surface of photosynthesising structures is related to the consumption of CO2 in photosynthesis. CO2 production by root respiration can solubilise soil CaCO3. A few cyanobacteria and eukaryotic algae can bore through solid CaCO3 by removing Ca2+ and adding H+ at the site of boring, generating soluble inorganic C that can be used in photosynthesis. Ca(COO)2 is precipitated in the vacuoles of many algae and plants, and the cell walls of some plants. An outcome of precipitation of CaCO3 using CO3= produced from CO2, and Ca2+, is the production of H+; the same is the case for precipitation of Ca(COO)2 from (COOH)2 and Ca2+. The H+ produced by Ca(COO2) can be used to neutralise OH− produced in NO3− assimilation in the shoot without increasing cell osmolarity. There is no evidence of CaCO3 fulfilling this role. Another outcome of CaCO3 and Ca(COO)2 precipitation is Ca2+ immobilisation, though with little evidence of remobilisation of Ca2+ under Ca2+ deficiency. Other consequences of CaCO3 and Ca(COO)2 precipitation are light scattering and increased density, and ‘alarm photosynthesis’. Defence against herbivores and pathogens is better established for Ca(COO)2 than for CaCO3, and pollen release from anthers is a function of Ca(COO)2 but not CaCO3.
The only possibility of obtaining information about what we will call the “objects” present in our environment is through our sense organs. They cannot detect life per se, but they are able to divide the objects they detect into two categories: non-living and living. Life can then be defined by “life is present where there is at least one living object”. The transition “non-living → living”, termed “spontaneous generation”, is impossible on the Earth as it is at present. By contrast, the transition “living → non-living”, termed “death”, is currently observed. A “criterion of life” can be obtained by observing the behavior of an unknown object under isolation vs. free contact with the outside. Since it is not possible for a living object to arise from a non-living object on the Earth as it is today, the beginning of the processes that were to lead to the first living object(s) must have occurred at the birth of the Earth (the epoch when it differed the most from what it is now). It was then much too hot for organic molecules to have existed there. Therefore, it is likely that the processes thus set in action first involved only mineral substances then evolved towards the acquisition of organic compounds as the Earth cooled. Hence it would have taken several hundred million years for the acquisition of the first protocells, finally followed over billions of years by their evolution into bacteria, animals and plants.
