Abstract
The understanding of acclimation strategies to low temperature and water availability is decisive to ensure coffee crop sustainability, since these environmental conditions determine the suitability of cultivation areas. In this context, the impacts of single and combined exposure to drought and cold were evaluated in three genotypes of the two major cropped species, Coffea arabica cv. Icatu, Coffea canephora cv. Apoatã, and the hybrid Obatã. Crucial traits of plant resilience to environmental stresses have been examined: photosynthesis, lipoperoxidation and the antioxidant response. Drought and/or cold promoted leaf dehydration, which was accompanied by stomatal and mesophyll limitations that impaired leaf C-assimilation in all genotypes. However, Icatu showed a lower impact upon stress exposure and a faster and complete photosynthetic recovery. Although lipoperoxidation was increased by drought (Icatu) and cold (all genotypes), it was greatly reduced by stress interaction, especially in Icatu. In fact, although the antioxidative system was reinforced under single drought and cold exposure (e.g., activity of enzymes as Cu,Zn-superoxide dismutase, ascorbate peroxidase, APX, glutathione reductase and catalase, CAT), the stronger increases were observed upon the simultaneous exposure to both stresses, which was accompanied with a transcriptional response of some genes, namely related to APX. Complementary, non-enzyme antioxidant molecules were promoted mostly by cold and the stress interaction, including α-tocopherol (in C. arabica plants), ascorbate (ASC), zeaxanthin, and phenolic compounds (all genotypes). In general, drought promoted antioxidant enzymes activity, whereas cold enhanced the synthesis of both enzyme and non-enzyme antioxidants, the latter likely related to a higher need of antioxidative capability when enzyme reactions were probably quite repressed by low temperature. Icatu showed the wider antioxidative capability, with the triggering of all studied antioxidative molecules by drought (except CAT), cold, and, particularly, stress interaction (except ASC), revealing a clear stress cross-tolerance. This justified the lower impacts on membrane lipoperoxidation and photosynthetic capacity under stress interaction conditions, related to a better ROS control. These findings are also relevant to coffee water management, showing that watering in the cold season should be largely avoided.
Highlights
It is widely recognized that abiotic stresses, such as extreme temperatures, drought, or salinity, are major limiting factors to agriculture sustainability, more than halving average yields for major crop species [1]
Droughted plants differed visually, with mild drought (MD) plants becoming wilted by the end of the diurnal period, whereas severe drought (SD) plants were permanently wilted along the diurnal period
This resulted in closer relative water content (RWC) values between the plants of RWC CW net photosynthetic rate (Pn) photosynthetic capacity (Amax) MDA Cu,Zn-superoxide dismutase (SOD) ascorbate peroxidase (APX) glutathione reductase (GR) CAT TOC ASC ZEA V+A+Z de-epoxidation state (DEPS) Total Phenols 5-caffeoylquinic acid (CQA)
Summary
It is widely recognized that abiotic stresses, such as extreme temperatures, drought, or salinity, are major limiting factors to agriculture sustainability, more than halving average yields for major crop species [1]. Multiple stressors (e.g., extreme temperatures and water shortage) are frequently superimposed, with plants responding in ways not directly predictable from each single stress condition. Low positive temperatures (usually below 10 ̊C) and water shortage affect photosynthesis, nutrient uptake, and crop yield, quality and post-harvest preservation [8,9]. Both stresses can affect virtually all photosynthetic components provoking, e.g., stomatal closure (reducing net photosynthesis and sugar metabolism), changes on pigment complexes, reduction of photochemical efficiency and enzymes activity. Chilling reduces chemical reactions, and affects the lipid matrix of membranes, namely at the chloroplast level, further impairing thylakoid electron transport [8,10,11]
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