Integrated physiological and hormonal profile of heat-induced thermotolerance inPinus radiata

Abstract

Despite great interest, not only from the economic point of view but also in terms of basic science, research on heat stress tolerance in conifers remains scarce. To fill this gap, a time-course experiment using expected temperature increase was performed aiming to identify physiological and biochemical traits that allow the characterization of heat-induced thermotolerance and recovery in Pinus radiata D. Don plants. Several physiological parameters were assessed during heat exposure and after recovery, and multiple phytohormones-abscisic acid (ABA), indole-3-acetic acid (IAA), cytokinins (CKs), gibberellins, jasmonic acid, salicylic acid (SA) and brassinosteroids-were quantified by ultra-performance liquid chromatography-mass spectrometry from unique sample. Furthermore, tissue specific stress-signaling was monitored by IAA and ABA immunolocalization. Multivariate statistical analysis of the data enabled clustering of the shorter- and longer-term effects of heat stress exposure. Two sequential physiological responses were identified: an immediate and a delayed response, essentially determined by specific phytohormones, proline, malondialdehyde and total soluble sugar patterns. Results showed that ABA and SA play a crucial role in the first stage of response to heat stress, probably due to the plant's urgent need to regulate stomatal closure and counteract the increase in oxidative membrane damage demonstrated in shorter-term exposures. However, in longer exposures and recovery, proline, total sugars, IAA and CKs seem to be more relevant. This integrated approach pinpointed some basic mechanisms of P. radiata physiological responses underlying thermotolerance processes and after recovery.

Cytokinin at the Crossroads of Abiotic Stress Signalling Pathways

“…A rapid proteomic heat-shock response that could be mimicked to some extent by cytokinin treatment at standard temperature has also been reported [136], indicating that cytokinin may play a role in temperature perception. Moreover, the accumulation of cytokinin has been observed in Pinus radiata under prolonged heat stress and in recovered plants [137,138]. Plants with increased levels of cytokinins show a higher accumulation of heat-shock proteins [107,139,140] and enhanced activity of the antioxidant system [88,112].…”

Impacts of leaf age and heat stress duration on photosynthetic gas exchange and foliar nonstructural carbohydrates in Coffea arabica

“…Escandón et al. (2016) also found that soluble sugars seemed more closely associated with plant responses to increasing number of days exposed to heat stress, although they did not measure starch. Interestingly, glucose + fructose was not significantly affected by day or treatment in the 45‐ and 90‐min groups (Figure 6), consistent with Lafta and Lorenzen (1995) that found no effect of temperature on sugar levels in potato and attributed this to coordinated control of sugar metabolism in response to high temperature stress.…”

“…However, the extent of damage as measured with photosynthesis at day 2 did not differ between leaf age classes nor treatment, suggesting that leaf age may influence the capacity to recover more than the extent of damage incurred, although both characteristics influence the ability to withstand heat stress (Escandón et al., 2016). Consistent with our second hypothesis, the 90‐min duration of heat stress resulted in both greater physiological damage and slower recovery than the 45‐min group as measured with F V / F M and slower recovery as measured with photosynthesis (Figure 1).…”

Populus euphratica: an incompatible host for biotrophic pathogens?

“…The effects of moderate heat stress on the leaf proteomes of P. euphratica plantlets in hydroponic culture were reported 10 years ago (Ferreira et al ., ) and, very recently, other authors have replicated some aspects of this experiment with Pi. radiata , but with a much diversified and interesting analytical test (Escandón et al ., ). Although Pi.…”

“…Therefore, its accumulation is not strictly dependent on VIO; instead, VIO abundance is dependent on ZEA conversion, but, as VDE activity is increased by electrolyte leakage at high temperature, the ZEA pool increases, whereas the VIO pool decreases, leaving less VIO to be ultimately converted into ABA. However, ABA and SA biosynthesis have been found to increase at high temperature in Pinus radiata (Escandón et al ., ), and moderate heat stress has been found to have a positive impact on net photosynthesis and growth. So, how are the xanthophyll cycle, ABA and SA related in acclimation to high temperature?…”