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Environmental abiotic constraints are known to reduce plant growth. This effect is largely due to the inhibition of cell division in the leaf and root meristems caused by perturbations of the cell cycle machinery. Progression of the cell cycle is regulated by CDK kinases whose phosphorylation activities are dependent on cyclin proteins. Recent results have emphasized the role of inhibitors of the cyclin-CDK complexes in the impairment of the cell cycle and the resulting growth inhibition under environmental constraints. Those cyclin-CDK inhibitors (CKIs) include the KRP and SIAMESE families of proteins. This review presents the current knowledge on how CKIs respond to environmental changes and on the role played by one subclass of CKIs, the SIAMESE RELATED proteins (SMRs), in the tolerance of plants to abiotic stresses. The SMRs could play a central role in adjusting the balance between growth and stress defenses in plants exposed to environmental stresses. [ABSTRACT FROM AUTHOR]

SUMMARY: With climate change, an aggravation in summer drought is expected in the Mediterranean region. To assess the impact of such a future scenario, we compared the response of Quercus pubescens, a drought‐resistant deciduous oak species, to long‐term amplified drought (AD) (partial rain exclusion in natura for 10 years) and natural drought (ND). We studied leaf physiological and physico‐chemical trait responses to ND and AD over the seasonal cycle, with a focus on chemical traits including major groups of central (photosynthetic pigments and plastoquinones) and specialized (tocochromanols, phenolic compounds, and cuticular waxes) metabolites. Seasonality was the main driver of all leaf traits, including cuticular triterpenoids, which were highly concentrated in summer, suggesting their importance to cope with drought and thermal stress periods. Under AD, trees not only reduced CO2 assimilation (−42%) in summer and leaf concentrations of some phenolic compounds and photosynthetic pigments (carotenoids from the xanthophyll cycle) but also enhanced the levels of other photosynthetic pigments (chlorophylls, lutein, and neoxanthin) and plastochromanol‐8, an antioxidant located in chloroplasts. Overall, the metabolomic adjustments across seasons and drought conditions reinforce the idea that Q. pubescens is highly resistant to drought although significant losses of antioxidant defenses and photoprotection were identified under AD. Significance Statement: Climate change will increase drought episodes, especially in the Mediterranean region. This study investigated Quercus pubescens response to long‐term amplified drought (AD) in natura, focusing on leaf physiological and physico‐chemical traits across seasons and AD. It revealed that seasonal variations influenced leaf metabolism, including leaf cuticular compounds, which are important to cope with drought and thermal stress. Also, AD led to a decrease in net photosynthesis as well as losses in antioxidant defense and photoprotection. [ABSTRACT FROM AUTHOR]

UV-B and UV-A radiation are natural components of solar radiation that can cause plant stress, as well as induce a range of acclimatory responses mediated by photoreceptors. UV-mediated accumulation of flavonoids and glucosinolates is well documented, but much less is known about UV effects on carotenoid content. Carotenoids are involved in a range of plant physiological processes, including photoprotection of the photosynthetic machinery. UV-induced changes in carotenoid profile were quantified in plants (Arabidopsis thaliana) exposed for up to ten days to supplemental UV radiation under growth chamber conditions. UV induces specific changes in carotenoid profile, including increases in antheraxanthin, neoxanthin, violaxanthin and lutein contents in leaves. The extent of induction was dependent on exposure duration. No individual UV-B (UVR8) or UV-A (Cryptochrome or Phototropin) photoreceptor was found to mediate this induction. Remarkably, UV-induced accumulation of violaxanthin could not be linked to protection of the photosynthetic machinery from UV damage, questioning the functional relevance of this UV response. Here, it is argued that plants exploit UV radiation as a proxy for other stressors. Thus, it is speculated that the function of UV-induced alterations in carotenoid profile is not UV protection, but rather protection against other environmental stressors such as high intensity visible light that will normally accompany UV radiation. [ABSTRACT FROM AUTHOR]

Plants, like most living organisms, spontaneously emit photons of visible light. This ultraweak endogenous chemiluminescence is linked to the oxidative metabolism, with lipid peroxidation constituting a major source of photons in plants. We imaged this signal using a very sensitive cooled CCD camera and analysed its spectral characteristics using bandpass interference filters. In vitro oxidation of lipids induced luminescence throughout the visible spectrum (450–850 nm). However, luminescence in the red spectral domain (>640 nm) occurred first, then declined in parallel with the appearance of the emission in the blue-green (<600 nm). This temporal separation suggests that the chemical species emitting in the blue-green are secondary products, possibly deriving from the red light-emitting species. This conversion did not seem to occur in planta because spontaneous chemiluminescence from plant tissues (leaves, roots) occurred only in the red/far-red light domain (>640 nm), peaking at 700–750 nm. The spectrum of plant chemiluminescence was independent of chlorophyll. The in vivo signal was modulated by cellular detoxification mechanisms and by changes in the concentration of singlet oxygen in the tissues, although the singlet oxygen luminescence bands did not appear as major bands in the spectra. Our results indicate that the intensity of endogenous chemiluminescence from plant tissues is determined by the balance between the formation of luminescent species through secondary reactions involving lipid peroxide-derived intermediates, including singlet oxygen, and their elimination by metabolizing processes. The kinetic aspects of plant chemiluminescence must be taken into account when using the signal as an oxidative stress marker. [ABSTRACT FROM AUTHOR]