The photoreceptors UV RESISTANCE LOCUS 8 (UVR8) and CRYPTOCHROMES 1 and 2 (CRYs) play major roles in the perception of UV-B (280–315 nm) and UV-A/blue radiation (315–500 nm), respectively. However, it is poorly understood how they function in sunlight. The roles of UVR8 and CRYs were assessed in a factorial experiment with Arabidopsis thaliana wild-type and photoreceptor mutants exposed to sunlight for 6 h or 12 h under five types of filters with cut-offs in UV and blue-light regions. Transcriptome-wide responses triggered by UV-B and UV-A wavelengths shorter than 350 nm (UV-A sw ) required UVR8 whereas those induced by blue and UV-A wavelengths longer than 350 nm (UV-A lw ) required CRYs. UVR8 modulated gene expression in response to blue light while lack of CRYs drastically enhanced gene expression in response to UV-B and UV-A sw . These results agree with our estimates of photons absorbed by these photoreceptors in sunlight and with in vitro monomerization of UVR8 by wavelengths up to 335 nm. Motif enrichment analysis predicted complex signaling downstream of UVR8 and CRYs. Our results highlight that it is important to use UV waveband definitions specific to plants’ photomorphogenesis as is routinely done in the visible region.

The UV-A/blue photoreceptors phototropins and cryptochromes are both known to contribute to stomatal opening (Δgs) in blue light. However, their relative contributions to the maintenance of gs in blue light through the whole photoperiod remain unknown. To elucidate this question, Arabidopsis phot1 phot2 and cry1 cry2 mutants (MTs) and their respective wild types (WTs) were irradiated with 200 μmolm-2s-1 of blue-, green- or red-light (BL, GL or RL) throughout a 11-h photoperiod. Stomatal conductance (gs) was higher under BL than under RL or GL. Under RL, gs was not affected by either of the photoreceptor mutations, but under GL gs was slightly lower in cry1 cry2 than its WT. Under BL, the presence of phototropins was essential for rapid stomatal opening at the beginning of the photoperiod, and maximal stomatal opening beyond 3 h of irradiation required both phototropins and cryptochromes. Time courses of whole-plant net carbon assimilation rate (Anet) and the effective quantum yield of PSII photochemistry (ΦPSII) were consistent with an Anet-independent contribution of BL on gs both in phot1 phot2 and cry1 cry2 mutants. The changing roles of phototropins and cryptochromes through the day may allow more flexible coordination between gs and Anet.

Key message Local adaptation largely segregates between traits affecting light responses and water relations, but population-level differences in stomatal conductance when growth is unconstrained converge among populations under water stress. Abstract Warming temperatures and altered precipitation patterns threaten plant populations worldwide. European beech ( Fagus sylvatica ) is a species that expresses both high phenotypic plasticity and local adaptation among populations. Beech seedlings’ susceptibility to prolonged drought may be dictated by their immediate light environment. We tested whether seedlings of four beech provenances, from contrasting edaphoclimatic environments, expressed differences in trait responses to imposed water stress under sun and shade treatments. Populations from the southern range margin were expected to display greater water-stress tolerance and core populations’ faster growth rates in the absence of abiotic limitations. Both high light and water stress induced differences in trait responses among provenances, but traits that failed to respond to our experimental treatments likewise did not segregate at the provenance level. Hence, those traits responding to light, e.g., increasing leaf flavonol index and leaf mass area, also tended to differ among provenances. Similarly, there was evidence of local adaptation among provenances in traits, like midday leaf water potential, responding to water stress. Exceptionally, there was a three way interaction water- × -light- × -provenance for stomatal conductance which converged among provenances under water stress. Leaf chlorophyll content also varied both with light and water in a provenance-specific manner. We found core provenances’ growth traits to outperform others under favourable conditions, whereas southern and high-elevation populations displayed traits adapted to tolerate high irradiance. Only stomatal conductance produced a complementary interactive response between light- × -water across provenances, whereas other traits responded less to combined water stress and high irradiance than to either treatment alone.

Cryptochromes (CRYs) and UV RESISTANCE LOCUS 8 (UVR8) photoreceptors perceive UV-A/blue (315-500 nm) and UV-B (280-315 nm) radiation in plants, respectively. While the roles of CRYs and UVR8 have been studied in separate controlled-environment experiments, little is known about the interaction between these photoreceptors. Here, Arabidopsis wild-type Ler, CRYs and UVR8 photoreceptor mutants (uvr8-2, cry1cry2 and cry1cry2uvr8-2), and a flavonoid biosynthesis-defective mutant (tt4) were grown in a sun simulator. Plants were exposed to filtered radiation for 17 d or for 6 h, to study the effects of blue, UV-A, and UV-B radiation. Both CRYs and UVR8 independently enabled growth and survival of plants under solar levels of UV, while their joint absence was lethal under UV-B. CRYs mediated gene expression under blue light. UVR8 mediated gene expression under UV-B radiation, and in the absence of CRYs, also under UV-A. This negative regulation of UVR8-mediated gene expression by CRYs was also observed for UV-B. The accumulation of flavonoids was also consistent with this interaction between CRYs and UVR8. In conclusion, we provide evidence for an antagonistic interaction between CRYs and UVR8 and a role of UVR8 in UV-A perception.

为探究不同土壤基质条件下核桃楸幼苗对干旱胁迫生理特性的响应,以两年生核桃楸幼苗为研究对象,在腐殖土、壤土和砂壤土三种基质条件下进行控水试验,水分梯度分别设置为CK(正常供水,80％田间持水量)、T1(轻度胁迫,60％田间持水量)、T2(中度胁迫,40％田间持水量)和T3(重度胁迫,20％田间持水量),测定幼苗叶片叶绿素、丙二醛、脯氨酸、抗氧化酶和光合指标.结果 表明,随着胁迫程度的加深,叶绿素含量和Chl a/b均呈逐渐降低的趋势(P＜0.05),在胁迫60d时,T3处理下的叶绿素a(Chl a)和叶绿素b(Chl b)分别比CK低65.41％和51.57％,3种基质中叶绿含量大小顺序为:腐殖土＞壤土＞砂壤土.随着胁迫程度的加深,叶片脯氨酸(Pro)、丙二醛(MDA)则呈逐渐升高的趋势(P＜0.05),胁迫60d时,砂壤土中T3处理的Pro含量最高为83.37mg·g-1,比CK高86.32％.腐殖土中幼苗叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性均随胁迫程度加深而升高,壤土中叶片SOD活性则呈先升高后降低的变化规律.3种土壤基质中核桃楸叶片净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)均随着胁迫程度的加深而降低,但不同基质中幼苗叶片的气孔限制和非气孔限制发生的时间不同,T3处理的叶片胞间CO2浓度(Ci)在腐殖土中是12:00时最低,而在壤土和砂壤土中则是10:00时最低.土壤全氮、全磷、渗透速率和蒸腾速率与叶绿素含量存在显著的正相关关系(P＜0.05),土壤容重与叶绿素含量存在显著的负相关关系(P＜0.05).因此,土壤基质和干旱胁迫对核桃楸幼苗的生理生化和光合特性产生了显著的影响,重度胁迫对幼苗的叶绿素、渗透物质和酶体系产生了严重的损伤,同时降低了核桃楸幼苗的光合生产力.总体上,腐殖土中的幼苗有着较好的抗旱表现.

Adansonia species, known by the common name “baobab,” have a very low regeneration rate in Madagascar. In order to determine if Malagasy Adansonia seedlings' vulnerability to drought may account for this low rate of regeneration, we compared growth, photosynthetic behavior and water use strategy of three species of Malagasy Adansonia (A. grandidieri, A. madagascariensis, A. rubrostipa). Our results indicated that drought depressed the growth, net assimilation rate, stomatal conductance and transpiration rate of Adansonia seedlings but increased their water use efficiencies. Adansonia species are able to withstand drought by reducing water loss through stomatal closure and their ability to store water within roots. Interspecific differences were attributed to diversity in water-use strategies, relative water content and biomass allocation. A. rubrostipa and A. grandidieri appeared to be more adapted to arid environments than A. madagascariensis. Ecological implications of these results are discussed.