Chloroplasts are commonly the site of the earliest abiotic injury visible in plant ultrastructure. In this study, six inbred lines of maize (Zea mays L.) were used to analyze changes in the ultrastructure of chloroplasts and related physiological parameters under conditions of drought stress simulated by 20% polyethylene glycol 6000 (-0.6 MPa) for three days. Chloroplasts of three maize lines proved to be more sensitive. They showed changes in ultrastructure in response to drought, including damage to thylakoid membranes, an increase in the number and size of plastoglobuli, swelling of thylakoid membranes both stromal and granal, disorganization of the thylakoid membrane system, an obvious increase in the intrathylakoid space, and a decrease in the length-to-width ratio and area of chloroplasts. In addition, the contents of malondialdehyde increased markedly in the sensitive lines. Contrary to the sensitive lines, stable structures and shapes in chloroplasts were observed in the drought-resistant lines; it could be considered as an advantage contributing to drought tolerance in the plants. In addition, the drought index of leaf fresh mass (LMDI) in drought-sensitive lines was ≤ 0.5, which was also associated with a lower content of leaf chlorophyll. In contrast, drought tolerance coincided with lesser growth reduction, and higher LMDI and leaf chlorophyll content.

Salicylic acid (SA) and nitric oxide (NO) form a new group of plant growth substances that cooperatively interact to promote plant growth and productivity. Water deficit (WD) stress is a major limiting factor for photosynthesis, which in turn limits crop yield. However, the mechanism of SA and NO in stimulating photosynthesis has not yet been elucidated. Therefore, in this study, we investigated the SA-and NO-mediated photosynthetic adaptability of maize seedlings to WD in terms of photosynthetic parameters, activities and mRNA levels of CO 2 assimilation enzymes. Our results showed that SA alleviated the WD-induced reduction of photosynthetic performance. The activities of Rubisco and Rubisco activase enzymes increased significantly due to SA pretreatment. Moreover, higher transcription rates of Rbc L, ZmRCAα and ZmRCAβ mRNA further confirmed the effects of SA on CO 2 assimilation. WD or SA-induced decreases or increases of CO 2 assimilation ability were further decreased after c-PTIO addition.

No abstract

To determine the role of melatonin in aging maize seeds ( Zea mays L.), we investigated the physiological characteristics and performance analysis of the transcriptome after applying melatonin to maize seeds as a response to aging. In this study, we demonstrated that applying exogenous melatonin alleviated aging-induced oxidative damage, improved the activity of aging seeds, promoted growth of the germ and radical, enhanced antioxidant enzyme activity and reduced membrane lipid peroxidation. In addition, transcriptome sequencing revealed that various metabolic processes were induced by exogenous melatonin application in aging maize seeds, including hormone signal transduction, cellular processes, carbohydrate metabolism, secondary metabolites, and amino acid metabolism. In summary, the findings provide a more comprehensive understanding for analyzing the protective effect of melatonin in aging maize seeds.

Photosynthesis is sensitive to water deficit (WD) stress. Maize (Zea mays L.) yield is vulnerable to water stress, especially if it occurs during the reproductive stage. In this study, the expression patterns of photosynthesis-related genes, together with photosynthetic gas-exchange and fluorescence parameters were investigated in a maize inbred line exposed to 50% of field water capacity (moderate WD) for 15 d after tassel emergence. The results demonstrated that WD down-regulated expression of psbA, psbB, psbC, psbP, psaA, psaB, and cab, especially at later periods of WD stress. Besides, with the increased WD stress, the steady decline in the value of photosynthesis performance index, maximum quantum yield of primary photochemistry, quantum yield for electron transport, quantum yield for the reduction of end acceptors of PSI per photon absorbed, and the efficiency of an electron beyond QA − that reduced PSI acceptors, and a clear increase in the J-step and I-step, K-band as well as L-band were observed. The results suggested that WD might restrict light-harvesting and electron transport. Interestingly, leaf transcript levels of rbcL and rbcS were up-regulated at the later stage of water stress in maize inbred line, which helped repair injury to PSII centers and maintain PSII activity (increased quantum yield of dissipation and effective antenna size of an active reaction center) under 15-d lasting WD.