Canola Responses to Drought, Heat, and Combined Stress: Shared and Specific Effects on Carbon Assimilation, Seed Yield, and Oil Composition

Abstract

Photosynthetic assimilation is remarkably altered by heat and drought, and this depends on the individual or combined occurrence of stressors and their respective intensities and durations. Abiotic stressors may also alter the nutritional quality and economic value of crops. In this controlled greenhouse study, we evaluated the response of Brassica napus L., from flowering to seed development, to two temperature and water treatments and a combination of these treatments. The diffusional limitations of stomatal conductance and mesophyll conductance on photosynthesis, as well as resource-use efficiency (particularly water and nitrogen), were assessed. In addition, the effects of stressors on the seed fatty acid content and composition and the total protein content were examined. The results showed that the reduction in the net photosynthetic assimilation rate was caused by combinations of heat and drought (heat + drought) treatments, by drought alone, and, to a lesser extent, by heat alone. The stomatal conductance decreased under drought and heat + drought treatments but not under heat. Conversely, the mesophyll conductance was reduced significantly in the plants exposed to heat and heat + drought but not in the plants exposed to drought alone. The carboxylation efficiency rate and the electron transport rate were reduced under the heat treatment. The seed yield was reduced by 85.3% under the heat treatment and, to a lesser extent, under the drought treatment (31%). This emphasizes the devastating effects of hotter weather on seed formation and development. Seed oil content decreased by 52% in the plants exposed to heat, the protein content increased under all the stress treatments. Heat treatment had a more deleterious effect than drought on the seed oil composition, leading to enhanced levels of saturated fatty oils and, consequently, desaturation efficiency, a measure of oil frying ability. Overall, this study showed that except for the photosynthetic assimilation rate and stomatal conductance, heat, rather than drought, negatively affected the photosynthetic capacity, yield, and oil quality attributes when imposed during the flowering and silique-filling stages. This result highlights the necessity for a better understanding of heat tolerance mechanisms in crops to help to create germplasms that are adapted to rapid climate warming.

High night‐time temperature during flowering and pod filling affects flower opening, yield and seed fatty acid composition in canola

“…However, Elferjani and Soolanayakanahally (2018) found an opposite response. Using 10 years of field data and following a modelling approach, Baux et al (2013) observed an increase in oleic acid (C18:1) in conventional oilseed rape and high-oleic low-linolenic (HOLL) varieties associated with minimum temperature, coincided by a decrease in linoleic acid (C18:2) and linolenic acids (C18:3) concentration.…”

“…Previous studies demonstrate that HDT stress during pod filling results in reduced oil concentration and increased protein concentration in oilseed crops (Aksouh-Harradj et al, 2006;Singer, Zou, & Weselake, 2016;Zhu et al, 2012 [canola]), (Dombos & Mullen, 1992;Gibson & Mullen, 1996 [soybean]). Similarly, a negative correlation between monounsaturated and polyunsaturated fatty acids has been observed with HDT stress exposure in a number of oilseed crops, including canola (Aksouh-Harradj et al, 2006;Baux et al, 2013;Deng & Scarth, 1998;Elferjani & Soolanayakanahally, 2018), sunflower (Nagao & Yamazaki, 1984;Flagella, Rotunno, Tarantino, Di Caterina, & De Caro, 2002) and soybean (Dornbos & Mullen, 1992;Gibson & Mullen, 1996). In summary, day-time heat stress is shown to alter the oil and protein composition and reduce beneficial monoand polyunsaturated fatty acids, while the impact of HNT on these fatty acids is not known either in canola or in other Brassica species.…”

“…Canola seed composition is significantly influenced by environmental conditions, particularly by temperature changes during seed development (Aksouh-Harradj, Campbell, & Mailer, 2006;Brunel-Muguet et al, 2015;Elferjani & Soolanayakanahally, 2018). The active phase of synthesis and storage of seed components in canola occurs between 2 and 5 weeks after the start of flowering (Chérif, 1983;Fowler & Downey, 1970;Rakow & McGregor, 1975), and this phase is considered to be vulnerable to high-temperature conditions.…”

Engineering Multiple Abiotic Stress Tolerance in Canola, Brassica napus

“…Different abiotic stresses adversely affect major biological processes in plants such as photosynthesis, stomatal conduction, rate of transpiration, protein synthesis, and metabolite accumulation (Zhang X. et al, 2014;Zhu et al, 2016;Elferjani and Soolanayakanahally, 2018). Abiotic stresses and their physiological consequences on plants are both shared and unique (Chinnusamy et al, 2004).…”

“…Grown in the temperate climates of both northern and southern hemispheres, it is cultivated in different seasons (annuals or biennials) (Shahzadi et al, 2015;Zhu et al, 2016). Just like other temperate field crops, B. napus is also susceptible to multiple abiotic stresses (Elferjani and Soolanayakanahally, 2018). Drought, salinity, extreme temperatures, and cadmium toxicity are the most prevalent abiotic stresses affecting the growth and development of B. napus.…”