Unraveling Main Limiting Sites of Photosynthesis under Below- and Above-Ground Heat Stress in Cucumber and the Alleviatory Role of Luffa Rootstock

Abstract

Photosynthesis is one of the most thermo-sensitive processes in plants. Although the severity of heat stress could be attenuated by grafting approach, the primary damaged site of photosynthesis system under heat stress and the regulatory mechanism of rootstock-mediated heat tolerance are poorly understood. In the current study, cucumber plants grafted onto their own roots and heat-tolerant luffa roots were exposed to root-zone heat (25/40°C) and aerial heat (40/25°C) individually and in combination (40/40°C) to understand the response of photosynthetic process by investigating energy absorption and distribution, electron transport in photosystem (PS) II and I, and CO2 assimilation. According to the results, root-zone heat stress inhibited photosynthesis mainly through decreasing Rubisco activity, while aerial heat stress mainly through inhibiting PSII acceptor side. The imbalance in light absorption and utilization resulted in accumulation of reactive oxygen species that caused damage to photosynthetic apparatus, forming a vicious cycle. On the contrary, grafting cucumber onto heat-tolerant luffa rootstock alleviated heat-induced photosynthetic inhibition and oxidative stress by maintaining higher root vitality, HSP70 accumulation, and antioxidant potential.

MdATG18a overexpression improves basal thermotolerance in transgenic apple by decreasing damage to chloroplasts

“…5). In general, PSII was more sensitive to high temperature than PSI 47 . For instance, a severe high temperature (43°C) had no remarkable effect on PSI photochemical capacity in sweet sorghum 48 .…”

COMT1 Silencing Aggravates Heat Stress-Induced Reduction in Photosynthesis by Decreasing Chlorophyll Content, Photosystem II Activity, and Electron Transport Efficiency in Tomato

“…Exposure of plants to high temperature stress decreases the rate of photosynthesis and the amount of photosynthetic pigments in leaves ( Shanmugam et al, 2013 ). Heat stress also causes water loss in aerial plant parts and impairs membrane integrity ( Li et al, 2015 ; Li H. et al, 2016 ). Both photosystems I and II (PSI and PSII) are affected by heat stress due to the heat-induced inhibition of light energy absorption, energy distribution, and electron transport ( Li H. et al, 2016 ).…”

Overexpression of CsCaM3 Improves High Temperature Tolerance in Cucumber

“…This influences normal growth, photosynthesis and fruit of cucumber plants seriously, causing premature aging, yield reduction, and diminished quality. The breeding of cucumbers for heat tolerance has been slow because of the scarcity of heat-tolerant genetic resources in the species, and in research of heat resistance in cucumber ( Ding et al, 2016 ; Li et al, 2016a , b ), in where few reports of transgenic CaM genes inserted into the cucumber genome for the purpose of increasing stress-tolerance. This study examined the overexpression of the CaM gene CsCaM3 in cucumber in order to enhance the heat tolerance of cucumber and provide the foundation for further improvements in the tolerance of cucumber plants to heat stress.…”