Response of linear and cyclic electron flux to moderate high temperature and high light stress in tomato

Objective： To evaluate the possible photoprotection mechanisms of cyclic and linear electron flux （CEF and LEF） under specific high temperature and high light （HH） stress. Methods： Six-leaf-stage tomato seedlings （＂Liaoyuanduoli＂, n=160） were divided into four parts： Part 1, served as control under 25 ℃, 500 pmol/（m2-s）; Part 2, spayed with distilled water （H20） under 35 ℃, 1000 pmol/（m2.s） （HH）; Part 3, spayed with 100 μmol/L diuron （DCMU, CEF inhibitor） under HH; Part 4, spayed with 60 pmol/L methyl viologen （MV, LEF inhibitor） under HH. Energy conversion, photosystem I （PSI）, and PSII activity, and trans-thylakoid membrane proton motive force were monitored during the treatment of 5 d and of the recovering 10 d. Results： HH decreased photochemical reaction dissipation （P） and the maximal photochemical efficiency of PSII （Fv/Fm）, and increased the excitation energy distribution coefficient of PSII （,8）; DCMU and MV aggravated the partition imbalance of the excitation energy （y） and the photoinhibition degree. With prolonged DCMU treatment time, electron transport rate and quantum efficiency of PSI （ETR= and Y1） significantly decreased whereas acceptor and donor side limitation of PSI （YNA and YND） increased. MV led to a significant decline and accession of yield of regulated and non-regulated energy Y NPQ and YNO, respectively. Membrane integrity and ATPase activity were reduced by HH stress, and DCMU and MV enhanced inhibitory actions. Conclusions： The protective effects of CEF and LEF were mediated to a certain degree by meliorations in energy absorption and distribution as well as by maintenance of thylakoid membrane integrity and ATPase activity.

Alteration of Sl YABBY2b gene expression impairs tomato ovary locule number and endogenous gibberellin content

Tomato is an ideal model species for fleshy fruit development research. Sl YABBY2 b regulates the ovary locule number, which is increased by gibberellins, in tomato. However, the relationship between Sl YABBY2 b and endogenous gibberellin is poorly understood. In this study, Sl YABBY2 b-overexpressing and RNA interference(RNAi) transgenic tomato plants were used to elucidate the mechanism by which Sl YABBY2 b regulates the ovary locule number and endogenous gibberellin content in tomato. Sl YABBY2 b-overexpressing plants showed fewer locules and lower gibberellin content than the control plants. Contrasting results were found in the RNAi lines. Therefore, the Sl YABBY2 b gene negatively regulates tomato ovary locule number and endogenous gibberellin content. Furthermore, the expression of Sl YABBY2 b gene was remarkably higher than that of the wild type in the apical shoots of gibberellindeficient mutants. This showed that the gibberellins can inhibit the expression of Sl YABBY2 b gene negative regulation. Further study revealed that Sl YABBY2 b suppressed the expression of Sl GA20 ox1 and Sl GA3 ox2, but increased that of Sl GA2 ox1 and Sl GA2 ox5 in the apical shoots of Sl YABBY2 b-overexpressing plants, thereby reducing gibberellin content. Contrasting results were found in the RNAi lines. Our results showed that the Sl YABBY2 b gene was located on gibberellin signal transduction pathways, fed back regulation of the synthesis of gibberellin, and felt exogenous gibberellin signal to further regulate the formation of tomato locule.