Studies On Mechanism And Effects On Enhancing Anti-chilling And Low Light Stress Of Different Chemical Substances On Facility Crop-tomato Seedlings

Even though China now boast the largest area of fertility horticulture in the world, most of them are simple type with very low level of environmental controlling; the capability of increasing and keeping the temperature in the greenhouse is very weak, so much that chilling are very frequent in the cold season. The photo permeability rate of the greenhouse and plastic shed can only get to 50%. To make things worse, the frequent sandy weather in northern China further lowers the photo permeability. Chilling and low light always happen together, which cause very serious consequences such as wilting, etiolation, freezing, dieing, root-rotting in the seedling period and flower dropping, fruit dropping, fruit withering in the flowering and fruit-bearing period. The measure against chilling and weak light include adopting new-type plastic film, clearing the film timely, opening and cover the grass curtain at regular time, installing light-reflecting aluminizing film or illuminating equipments to increase light intensity etc.. These measures are either troublesome or costly. By contrast, application of chemicals against chilling and low light, if possible, can be much convenient and time and labor-saving.Research shows that applying some exogenous chemical substances such as Ca²⁺,ABA(abscisicacid),GB (Glycine Betaine), CC (Choline Chloride) etc. can enhance the resistance ability of plants against chilling, which function through three mechanics as follows: first, increase the stability of the cellular membrane under chilling, second, function in the signal transduction of chilling and induce expression of cold-resist genes, third, as a osmotic substance, keep the water balance inside and outside the cell and maintain natural condition of the cell. ALA (5-Aminolevulinic Acid), a newly-developed plant active substance, as a necessary precursor for all porphyrin compound, play a significant role in the synthesis of chlorophyll and can increase the net photosynthesis rate, furthermore it can enhance plant against chilling and low light.In this study, four-leaved tomato seedlings, as the testing material, were sprayed with solutions of CaCl₂,GB,ALA of different concentrations then treated with chilling and low light simultaneously. By measuring the net photosynthetic rate, conductivity of stomata and calculating the chilling-induce-wilting index, 1mmol/L of CaCl₂, 2.5mmol/L of GB, 30mg/L of ALA were selected as effective concentration. Further experiment shows the function of the 3 chemicals towards single chilling and single low light are different. CaCl₂ mainly functions against the single chilling while ALA mainly contributes to photosynthesis under low light. Combining these 3 chemicals with different proportion into 8 formulas, formula IV was selected as the most effective through testing on four-leaved tomato seedlings.Chilling and low light damage plant in many ways, first, it damages the cellular membrane system and increases the leakage rate of electrolyte; second, it destroys antioxidant enzymes system, which cause the lipid peroxidation and accumulation of activate oxygen, third, it affect the level of osmotic regulator; last, low light can cause decrease of chlorophyll content in plant and the ratio of chlorophyll a/b. This study demonstrate that ALA, GB, CaCl₂ of appropriate concentration can alleviate the electrolyte leakage of the tomato seedlings under chilling and low light, and keep the stability of the membrane system. Chilling can lower the activity of SOD and accumulate MDA, This study shows that application of ALA, GB, CaC12 of appropriate concentration can keep the activity of SOD high of tomato seedlings under chilling and low light and keep low level of MDA simultaneously; activity of SOD and MDA content are of significantly negative correlation. Proline and soluable sugar, two major osmotic regulators, play very important roles in the anti-chilling of plant. This study shows that application of ALA, GB, CaCl₂ can help keep high level of praline and soluable sugar in the leaf. Besides, application of the above substances can help keep the level of total chlorophyll high and decrease the ratio of chlorophyll a/b, which exert a very critical function in improving the light-harvesting capability of LHP1 and enhancing the electron-transmitting efficiency of electron-transmitting chain, further increase the photosynthesis of plants under adverse conditions.