Heat-tolerant hot pepper exhibits constant photosynthesis via increased transpiration rate, high proline content and fast recovery in heat stress condition

Abstract

Understanding the mechanism for heat tolerance is important for the hot pepper breeding program to develop heat-tolerant cultivars in changing climate. This study was conducted to investigate physiological and biochemical parameters related to heat tolerance and to determine leaf heat damage levels critical for selecting heat-tolerant genotypes. Seedlings of two commercial cultivars, heat-tolerant ‘NW Bigarim’ (NB) and susceptible ‘Chyung Yang’ (CY), were grown in 42 °C for ten days. Photosynthesis, electrolyte conductivity, proline content were measured among seedlings during heat treatment. Photosynthetic rate was significantly reduced in ‘CY’ but not in ‘NB’ seedlings in 42 °C. Stomatal conductivity and transpiration rate was significantly higher in ‘NB’ than ‘CY’. Proline content was also significantly higher in ‘NB’. After heat treatment, leaf heat damages were determined as 0, 25, 50 and 75% and plants with different leaf heat damages were moved to a glasshouse (30–32/22–24 °C in day/night). The growth and developmental parameters were investigated until 70 days. ‘NB’ was significantly affected by leaf heat damages only in fruit yield while ‘CY’ was in fruit set, number and yield. ‘NB’ showed fast recovery after heat stress compared to ‘CY’. These results suggest that constant photosynthetic rate via increased transpiration rate as well as high proline content in heat stress condition confer faster recovery from heat damage of heat-tolerant cultivars in seedlings stages.

Heat-tolerant pepper cultivar exhibits high rates of chlorophyll, photosynthesis, stomatal conductance and transpiration in heat stress regime at fruit developing stage

“…The significant degradation of CHL in leaves at HT condition was observed more in heat susceptible genotype HT7 than heat tolerant HT1 and HT37. This is in agreement with observations in Solanaceae plants [6,9,12,14].…”

“…The leaf chamber temperature was 25°C, and the CO 2 concentration was 400 μmol (CO2) mol -1 . The photosynthetic rate was measured automatically after 3-4 min light exposure [6,13]. Data were recorded in four plants from fully expanded 3rd or 4th leaves from the top of the stem axis from each cultivar.…”

“…And, this is possibly due to the higher rates of CHL and photosynthetic activity such as Pn, Gs and Tr in a heat-tolerant cultivars at seedling growth stages through the entire days of HT than those in heat-susceptible cultivars [9]. It has been also reported that constant photosynthetic rate via increased transpiration rate as well as high proline content in heat stress condition confers fast recovery from heat damage of heat-tolerant cultivars at seedlings stages of pepper [6]. Moreover, it has been confirmed that grafting a pepper cultivar onto appropriate rootstocks can overcome the negative effects of heat stress conditions with a higher relative growth rate, leaf area and Fv/Fm, lower electrolyte leakage under the controlled conditions, and higher marketable yields under the greenhouse conditions [10].…”

“…Pepper (Capsicum annuum L.) is considered as an agriculturally important vegetable of global significance. However, high sub-optimal temperatures over 30 °C frequently influence physiological traits and reduce the productivity of Capsicum species [4][5][6]. Meanwhile, the reproductive traits of pepper cultivars have been changed by the high temperature, since the mechanisms controlling heat stress response in plants are complex and the response of cultivars as well as their physiological and biochemical parameters on the high temperature is different and may vary in growth stages [4,7,8].…”

“…Recently, it has been found that different heat damage levels of tomato leaf [9] and pepper plants [6] significantly affect the vegetative parameters at recovery, where faster recovery was identified in a heat-tolerant cultivar than susceptible one. And, this is possibly due to the higher rates of CHL and photosynthetic activity such as Pn, Gs and Tr in a heat-tolerant cultivars at seedling growth stages through the entire days of HT than those in heat-susceptible cultivars [9].…”