Heat stress has become an increasingly important factor in limiting wheat yields. In northernChina, high temperature (>30 °C) during the grain filling is one of the major constraints in increasing wheat productivity. We used two winter wheat (Triticum aestivumL.) cultivars with different sensitivities to heat stress (Jimai 22 ‘JM22’, low sensitivity and Xinmai 26 ‘XM26’, high sensitivity) to study the various aspects of photosynthetic characteristics during the grain filling stage under heat stress. The results showed that photosynthesis rates (P_n) in flag leaves ofXM26 decreased faster than inJM22 under heat stress during the grain‐filling stage.P_ndecreased more rapidly under heat stress than without stress, by up to 69.9% and 59.3%, respectively, at 10 days following heat stress (10DAS). This decline ofP_nwas not caused by heat‐induced stomatal limitation, but rather by a decline in Rubisco activity and a functional drop in photosystemII(PSII). After heat stress, the grain yield ofJM22 decreased by 6.41%, butXM26 decreased by 11.43%, when compared with their respective controls. Heat stress also caused an alteration of mesophyll cell ultrastructure. Injury caused by heat stress to organelles inXM26 was more severe thanJM22. Moreover, theJM22 cultivar showed some self‐repair capacity following heat stress injury. These results indicate that declines in photosynthetic performance caused by heat stress were cultivar‐dependent. Compared withXM26, theJM22 cultivar had superior heat stability in terms ofPSIIfunction and carboxylation activity, both of which are susceptible to heat stress.

Background: Soil salt stress is a problem in the world, which turns into one of the main limiting factors hindering maize production. Salinity significantly affects root physiological processes in maize plants. There are few studies, however, that analyses the response of maize to salt stress in terms of the development of root anatomy and respiration.Results: We found that the leaf relative water content, photosynthetic characteristics, and catalase activity exhibited a significantly decrease of salt stress treatments. However, salt stress treatments caused the superoxide dismutase activity, peroxidase activity, malondialdehyde content, Na⁺uptake and translocation rate to be higher than that of control treatments. The detrimental effect of salt stress on YY7 variety was more pronounced than that of JNY658. Under salt stress, the number of root cortical aerenchyma in salt-tolerant JNY658 plants was significantly higher than that of control, as well as a larger cortical cell size and a lower root cortical cell file number, all of which help to maintain higher biomass. The total respiration rate of two varieties exposed to salt stress was lower than that of control treatment, while the alternate oxidative respiration rate was higher, and the root response of JNY658 plants was significant. Under salt stress, the roots net Na⁺and K⁺efflux rates of two varieties were higher than those of the control treatment, where the strength of net Na⁺efflux rate from the roots of JNY658 plants and the net K⁺efflux rate from roots of YY7 plants was remarkable. The increase in efflux rates reduced the Na⁺toxicity of the root and helped to maintain its ion balance.Conclusion: These results demonstrated that salt-tolerant maize varieties incur a relatively low metabolic cost required to establish a higher root cortical aerenchyma, larger cortical cell size and lower root cortical cell file number, significantly reduced the total respiration rate, and that it also increased the alternate oxidative respiration rate, thereby counteracting the detrimental effect of oxidative damage on root respiration of root growth. In addition, Na⁺uptake on the root surface decreased, the translocation of Na⁺to the rest of the plant was constrained and the level of Na⁺accumulation in leaves significantly reduced under salt stress, thus preempting salt-stress induced impediments to the formation of shoot biomass.