Effects of brassinosteroid and brassinosteroid mimic on photosynthetic efficiency and rice yield under heat stress

Abstract

Brassinosteroids (BRs) have been reported to counteract various stresses. We investigated effects of exogenously applied brassinosteroid, 24-epibrassinolide (EBR), and brassinosteroid-mimic compound, 7,8-dihydro-8-20-hydroxyecdysone (DHECD), on the photosynthetic efficiency and yield of rice (Oryza sativa L. cv. Pathum Thani 1) under heat stress. Solutions (1 nM) of EBR and DHECD were separately sprayed onto foliage of individual rice plants during their reproductive stage. Five days after the application, the plants were transferred to the day/night temperature regime of 40/30ºC for 7 days and then allowed to recover at normal temperature for 7 days. We demonstrated that both DHECD and EBR helped maintain the net photosynthetic rate. The DHECD and EBR application enhanced stomatal conductance, stomatal limitation, and water-use efficiency under the high-temperature regime. DHECD-and EBR-treated plants showed an increase in the nonphotochemical quenching that was lower than that in the control plants. Moreover, DHECD and EBR treatments maintained the maximal quantum efficiency of PSII photochemistry and the efficiency of excitation capture of the open PSII center. Furthermore, the treatments with DHECD or EBR resulted in higher chlorophyll content during the heat treatment compared with the control plants. The paddy field application of 1 nM EBR and/or 1 nM DHECD at the reproductive stage during the hot season could increase the rice yield, especially, the number of filled seeds. DHECD and EBR enhanced total soluble sugar and reducing sugar in straw and more starch was accumulated in rice seeds. Consequently, our results confirmed that DHECD showed biological activities mimicking EBR in the improvement of photosynthetic efficiency and in rising the rice yield under heat stress.

Brassinosteroids improve photosystem II efficiency, gas exchange, antioxidant enzymes and growth of cowpea plants exposed to water deficit

“…Rajasekar et al (2016) observed a reduction in the photosynthetic pigments of Zea mays plants after a water deficit. Corroborating our study, Thussagunpanit et al (2015b) observed increases in Chl a, Chl b, total chl and Car after the application of EBR to Oryza sativa plants subjected to heat stress (47°C) for 7 days.…”

Physiological and molecular mechanisms of brassinosteroid-induced tolerance to high and low temperature in plants

“…In eggplant seedlings exposed to 43/38 °C for 8 d, pretreatment with 0.1 μM 24-epibrassinolide increased the content of chlorophyll a, b, and (a+b) by 17, 27, and 20 %, respectively, compared to heat-exposed plants that were not BR-treated (Wu et al 2014b). The decrease in chlorophyll content was milder in rice supplemented with 24-epibrassinolide prior to exposure to 40/30 °C for 7 d relative to the control (Thussagunpanit et al 2015a). In another study, this rice cultivar treated with 24-epibrassinolide showed an increase in the content of chlorophyll a, b, and (a+b) and carotenoids by 86, 74, 83, and 28 %, respectively, on the 7 th day of a high temperature exposure, compared to plants that were not treated with BR (Thussagunpanit et al 2015 b).…”

“…In the same cultivar grown in the field during the hot season, 24-epibrassinolide increased the total soluble sugar content in the straw (by 107 %). The hormone also increased reducing sugar content in the straw (by 72 %) and the starch content in the straw (by 27 %), husk (by 24 %), and seeds (by 35 %) (Thussagunpanit et al 2015a). Another rice cultivar exposed to a temperature of 35/32 °C for 12 h also demonstrated a decrease in the content of soluble sugars, which was further reduced by a mixture of plant growth regulators containing BRs (Fahad et al 2016).…”

“…The minimum fluorescence (F 0 ) was lower in plants that were sprayed with 24-epibrassinolide before stress, and parameters such as F m , F v /F m , F v '/F m ' had higher values than those noted in the stressed plants without BR application. The electron transport rate (ETR) in plants treated with 24-epibrassinolide was also significantly improved (Thussagunpanit et al 2015a). An analysis of chlorophyll a fast fluorescence kinetics in spring barley exposed to 42 °C (3 h) indicated an abnormal energy flow in PS II that was manifested in a decrease in energy absorption (ABS/CSm), energy flux for trapping (TRo/CSm), and energy flux for electron transport (ETo/CSm) (Janeczko et al 2011).…”

The physiological and molecular mechanism of brassinosteroid in response to stress: a review

“…Earlier studies showed that BR significantly increase yield and yield components of mustard plant [ 6 ]. Foliar application and seed treatments of BR significantly enhanced growth of tomato, as well as number of fruits and weight per plant; the yield of pear and yellow passion fruit are also improved by BR application [ 64 , 65 ]. Previous studies reported that BR played a positive role in fruit ripening and fruit growth of mango, and in the quality of pitaya [ 64 , 66 ].…”