| Wheat is one of the main food crops in the world, and it is also one of the important economic crops in China. Wheat plants are often subjected to high temperature stress caused by the global warming. Trehalose is believed to improve the tolerance of plants in many researches. However, in some reports, trehalose has been shown to have adverse effects on the growth of plants, and the reasons for these adverse effects are still unknown. In this paper, the effects of exogenously-supplied trehalose pretreatment on wheat growth, the contents of endogenous plant hormones and the expressions of the genes involved in hormone metabolism and cell cycle under heat stress were measured, to provide a theoretical basis for better research and utilization of trehalose by exploring the mechanism of trehalose to mitigate the growth of wheat.The main results are as follow:1 Exogenously-supplied trehalose pretreatment slowed down the growth of wheatHigh temperature stress decreased the dry weight of aerial part of wheat. Exogenously-supplied trehalose pretreatment decreased the stem height, root length and dry weight of wheat. It showed that trehalose had adverse effects on wheat, and slowed down the growth of wheat seedlings.2 Exogenously-supplied trehalose pretreatment changed the level of endogenous plant hormoneUnder normal temperature conditions, the exogenously-supplied trehalose pretreatment decreased the contents of the hormones which could promote the growth of wheat, such as IAA, ZT and GA3. High temperature stress reduced the content of IAA and ZT in wheat leaves, while the contents of IAA and ZT in trehalose pretreatment group were lower, suggest the influence of trehalose on the contents of IAA, ZT and GA3 has occurred before high temperature stress; under high temperature stress, the contents of these three hormones did not continue to decline, but still lower than the control plants. Under high temperature stress, the exogenously-supplied trehalose pretreatment did not affect the content of ABA, but at recovery stage, the content of ABA was significantly higher than that in the control plants.The effect of trehalose on the hormones in root was different from that in leaves. Trehalose pretreatment reduced the contents of IAA, ZT and ABA at room temperature. The exogenously-supplied trehalose pretreatment decreased the contents of IAA, ZT and ABA under normal growth condition. Under high temperature stress, the contents of ABA and ZT remained a downward trend and showed more decrease in trehalose pretreated wheat seedlings compared with control plants, but the content of IAA was higher in trehalose pretreated wheat seedlings. However, under normal growth and high temperature condition, the content of GA3 was not affected by trehalose pretreatment.These changes suggested that the reason why high temperature and exogenously-supplied trehalose inhibited wheat growth may be due to the decline in the levels of these hormones, such as IAA, ZT and GA3, which could promote the growth.3 Exogenously-supplied trehalose pretreatment changed the contents of hormones by affecting their synthesis and decompositionUnder the normal growth conditions, the expression of YUC gene in exogenously-supplied trehalose pretreatment was lower than that of the control group, and IAA oxidase activity was higher than control group, indicating that trehalose, by reducing the IAA synthesis and accelerating its degradation, decreased the content of IAA in wheat under the normal growth conditions. The high temperature stress reduced the expression of the YUC gene in wheat, while no difference was obtained between exogenously-supplied trehalose pretreatment and control plants. The changes of IAA oxidase activity, showed that exogenously-supplied trehalose decreased IAA content in leaves by accelerating the degradation of IAA under high temperature stress. NCED and CYP regulate the synthesis and degradation of ABA respectively. Exogenously-supplied trehalose pretreatment decreased the expressions of NCED and CYP, and this may be why the change of ABA content showed no obvious differences under the room temperature and high temperature conditions.4 Exogenously-supplied trehalose pretreatment reduced the expressions of genes involved in cell cycleExogenously-supplied trehalose pretreatment down-regulated the expressions of CycD2 and CDC2 genes. High temperature stress enhanced the degree of this reduction, indicating that high temperature and trehalose affected the cell cycle progression by regulating the expressions of cell cycle genes, and resulted in the slower growth of wheat.5 Exogenously-supplied trehalose pretreatment affected cell extension by reducing the activity of vacuolar invertaseUnder high temperature stress, the vacuolar invertase activity in the leaves was decreased, and during recovery phase, it was increased. Under normal growth condition, the vacuolar invertase activity in those trehalose pretreated wheat seedlings was much more lower than that in control plants. Under high temperature condition, the activity of vacuolar invertase maintained the downward trend, but the vacuolar invertase activity showed no obvious differences between trehalose pretretment plants and control plants. In the recovery phase, the vacuolar invertase activity in these two treated plants was increased, but it in trehalose pretretment plants were significantly lower than it in the control plants. Besides, the change trend of the vacuolar invertase activity was coherent with the change trend of cell length, which showed that trehalose pretretment affected the extension of the cell by reducing the activity of the vacuolar invertase activity, thereby the cell length was reduced.In conclusion, this paper showed that exogenously-supplied trehalose regulated the gene expressions and enzyme activity in the hormone metabolism pathways, so that the contents of IAA, ZT and GA3 in wheat under normal growth conditions were decreased. At the same time, the relative expressions of the key genes in cell cycle, CycD2 and CDC2, down-regulated in exogenously-supplied trehalose pretreated plants. Trehalose pretretment reduced the activity of vacuolar invertase and decreased the length of the cell. That is to say, the growth of wheat was regulated by trehalose from two aspects, namely the regulation of hormone level and cell proliferation and extension under normal and high temperature conditions. |
PDF Full Text Request