Heat stress has become an increasingly important factor in limiting wheat yields. In northern China, high temperature (>30°C) during the grain filling is one of the major constraints in increasing wheat productivity. We used two winter wheat (Triticum aestivum L.) 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 of XM26 decreased faster than in JM22 under heat stress during the grain-filling stage. P n decreased more rapidly under heat stress than without stress, by up to 69.9% and 59.3%, respectively, at 10 days following heat stress (10 DAS). This decline of P n was not caused by heat-induced stomatal limitation, but rather by a decline in Rubisco activity and a functional drop in photosystem II (PSII). After heat stress, the grain yield of JM22 decreased by 6.41%, but XM26 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 in XM26 was more severe than JM22. Moreover, the JM22 cultivar showed some self-repair capacity following heat stress injury. These results indicate that declines in photosynthetic performance caused by heat stress were cultivardependent. Compared with XM26, the JM22 cultivar had superior heat stability in terms of PSII function and carboxylation activity, both of which are susceptible to heat stress.
Summary Recently, samples of the Chinese tallow tree (Sapium sebiferum) displaying yellowing symptoms were collected from a grove in Tai'an, Shandong Province, China. The association of phytoplasma with yellowing disease was ascertained using nested polymerase chain reaction (PCR) of the 16S rRNA gene by using the phytoplasma‐specific universal primer pair P1/P7, followed by R16F2n/R16R2 as nested primers, and rp genes primed using rpL2F3/rp(I)R1A followed by rp(III)‐FN/rp(I)R1A. The sequence and phylogenetic analyses of the 16S rRNA gene and rp genes revealed that the phytoplasma associated with the Chinese tallow tree belonged to the 16SrIII group (the X‐disease group). Computer‐simulated and gel‐based restriction fragment length polymorphism (RFLP) analyses revealed that the RFLP patterns were different from the reference patterns of all previously established 16SrIII subgroups, with the maximum similarity coefficient exceeding the threshold for delineation of a new subgroup RFLP pattern type within the 16SrIII group. Thus, the phytoplasma associated with the Chinese tallow tree yellowing disease, designated as ‘CTTY’, represents a new subgroup (16SrIII‐Y). This study shows the Chinese tallow tree as a new host of phytoplasma belonging to the 16SrIII group in China and worldwide.
The mitogen‐activated protein kinase (MAPK) cascade pathway is a ubiquitous signal transduction pathway in eukaryotes that regulates a variety of immune responses. This study accomplished the first isolation of an AccMKK4 gene from Apis cerana cerana and explored its function. Yeast two‐hybrid experiments proved that AccMKK4 can interact with Accp38b, and the silencing of AccMKK4 in honeybees downregulated the expression level of Accp38b, which suggests that AccMKK4 might participate in the oxidative stress response through the p38 MAPK pathway. Tissue‐specific expression levels of AccMKK4 analysis showed that AccMKK4 in the thorax, particularly muscle tissue, was higher than that in other tissues. The qRT‐PCR results from different conditions demonstrated that AccMKK4 responds to various environmental stresses. After AccMKK4 silencing, the transcription level of some antioxidant genes and the activity of antioxidant‐related enzymes are reduced, which indicated that AccMKK4 plays an important role in resistance against oxidative stress caused by external stimuli. In summary, our findings indicate that AccMKK4 probably plays an indispensable role in the response of honeybees to environmental stress and might aid for further research on the role of the MAPK cascade pathway in the antioxidant defence mechanisms of insects.
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