High temperature and high light intensity is a common environment posing a great risk to organisms. This study aimed to elucidate the effects of sub-high temperature and high light stress (HH, 35°C, 1000 μmol∙m-2∙s-1) and recovery on the photosynthetic mechanism, photoinhibiton of photosystem II (PSII) and photosystem I (PSI), and reactive oxygen (ROS) metabolism of tomato seedlings. The results showed that with prolonged stress time, net photosynthetic rate (Pn), Rubisco activity, maximal photochemistry efficiency (Fv/Fm), efficient quantum yield and electron transport of PSII [Y(II) and ETR(II)] and PSI [Y(I) and ETR(I)] decreased significantly whereas yield of non-regulated and regulated energy dissipation of PSII [Y(NO) and Y(NPQ)] increased sharply. The donor side limitation of PSI [Y(ND)] increased but the acceptor side limitation of PSI [Y(NA)] decreased. Content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) were increased while activity of superoxide dismutase (SOD) and peroxidase (POD) were significantly inhibited compared to control. HH exposure affected photosynthetic carbon assimilation, multiple sites in PSII and PSI, ROS accumulation and elimination of Solanum lycopersicum L.

Melatonin (MT) can protect plants against abiotic stress. In order to explore whether melatonin can improve photosynthetic function under NaCl stress, Solanum lycopersicum L. cv. Liaoyuanduoli were exposed to 150 mmol L⁻¹ NaCl stress with or without pretreatment with 150 μmol L⁻¹ melatonin. The results showed that NaCl stress can lead to reduced chlorophyll content, lower photosynthetic function, increased reaction oxygen species (ROS) levels, and decreased PSII activity. These changes were mainly due to the reduction in oxygen-evolving complex (OEC) activity on the donor side of PSII and the blockage of electron transfer from Q_A to Q_B on receptor side of PSII. The donor side of PSII was more sensitive to NaCl stress relative to the receptor side of PSII. Interestingly, application of MT enhanced tomato NaCl tolerance. MT reduced the production of ROS by balancing the distribution of photosynthetic electron flux, facilitated the repair of PSII by maintaining the abundance of Psb O and D1, and promoting the ability of the donor and acceptor sides of PSII to deliver electrons. MT also enhanced the scavenging ability of ROS by stimulating the activity of enzymes involved in the AsA-GSH cycle.

Ethylene perception is regulated by receptors, and the downstream protein CONSTITUTIVE TRIPLE RESPONSE1 is a key suppressor of ethylene signalling. The non-conserved tomato (Solanum lycopersicum) microRNA1917 (Sly-miR1917) mediates degradation of SlCTR4 splice variants (SlCTR4sv) but the molecular details of this pathway remain unknown. Sly-miR1917 and the targeted SlCTR4sv are ubiquitously expressed in all tomato organs. Overexpression of Sly-miR1917 enhances ethylene responses, including the triple response in etiolated seedlings, in the absence of ethylene, as well as epinastic petiole growth, accelerated pedicel abscission, and fruit ripening. Enhanced ethylene signalling in Sly-miR1917-overexpressing plants (1917-OE) is accompanied by up-regulation of ethylene biosynthesis and signalling genes, and increased ethylene emission. These phenotypes were recovered by repressing the positive ethylene regulator EIN2. Moreover, the Sly-miR1917-targeted SlCTR4 splice variant SlCTR4sv3, expressed specifically in the abscission zone, exhibited the opposite expression pattern to Sly-miR1917. Complementation of the Arabidopsis thaliana ctr-1 mutant and yeast two-hybrid and bimolecular fluorescence complementation assays suggested that SlCTR4sv3 functions in ethylene signalling. Co-expression of Sly-miR1917 and SlCTR4sv3 in Nicotiana benthamiana further suggested that Sly-miR1917 cleaves SlCTR4sv3 in vivo. Database homology searching revealed a Solanum tuberosum CTR-like splice variant containing a Sly-miR1917 binding sequence, and a homologue of mature Sly-miR1917 in potato, indicating a conserved function for miR1917 and the regulatory miRNA-mediated ethylene network in solanaceous species.

As one of the grave environmental hazards, soil salinization seriously limits crop productivity, growth, and development. When plants are exposed to salt stress, they suffer a sequence of damage mainly caused by osmotic stress, ion toxicity, and subsequently oxidative stress. As sessile organisms, plants have developed many physiological and biochemical strategies to mitigate the impact of salt stress. These strategies include altering root development direction, shortening the life cycle, accelerating dormancy, closing stomata to reduce transpiration, and decreasing biomass. Apart from being a prime energy source, light is an environmental signal that profoundly influences plant growth and development and also participates in plants' response to salt stress. This review summarizes the regulatory network of salt tolerance by light signals in plants, which is vital to further understanding plants' adaptation to high salinity. In addition, the review highlights potential future uses of genetic engineering and light supplement technology by light-emitting diode (LED) to improve crop growth in saline–alkali environments in order to make full use of the vast saline land.

In many fruiting plant species, flower abscission is induced by low light stress. Here, we elucidated how signaling mediated by the peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) controls low light-induced flower drop in tomato (Solanum lycopersicum). We analyzed the expression patterns of an IDA-Like gene (SlIDL6) during low light-induced flower abscission, and used tandem mass spectrometry to identify and characterize the mature SlIDL6 peptide. Tomato knockout lines were created to investigate the in vivo function of SlIDL6. In addition, yeast one-hybrid assays were used to investigate the binding of the SlWRKY17 transcription factor to the SlIDL6 promoter, and silencing of SlWRKY17 expression delayed low light-induced flower abscission. SlIDL6 was specifically expressed in the abscission zone and at high levels during low light-induced abscission and ethylene treatment. SlIDL6 knockout lines showed delayed low light-induced flower drop, and the application of SlIDL6 peptide accelerated abscission. Overexpression of SlIDL6 rescued the ida mutant phenotype in Arabidopsis (Arabidopsis thaliana), suggesting functional conservation between species. SlIDL6-mediated abscission was via an ethylene-independent pathway. We report a SlWRKY17-SlIDL6 regulatory module that functions in low light promoted abscission by increasing the expression of enzymes involved in cell wall remodeling and disassembly.