大强度去叶对棉花叶绿素和保护酶系的影响

Activities of chlorophyll and protective enzyme systems in cotton plants Gossypium hirsutum L.with heavy leaf removal by no overcompensation

研究了大强度去叶对棉花叶绿素和保护酶系的影响。结果表明,75%去叶和100%去叶的大强度去叶不会促使棉花产生超补偿现象,而使棉花成铃数分别减少5.4%和9.8%。在短期内大强度去叶可使棉花新生叶片增大、叶绿素含量下降。75%去叶和100%去叶处理还使得棉花叶中蛋白质含量下降,POD酶活性上升、PPO酶活性下降,但POD酶比活力和PPO酶的比活力都上升。说明大强度去叶不仅对植物造成了严重伤害,而且破坏了棉花植株的内稳态平衡。植物不能迅速调整内稳态平衡(homeostasis)恢复元气,最终棉花也不会产生超补偿现象,此时植物处于伤害状态。内稳态变化可能存在信号分子。

When 8 squares are removed from each cotton plant, simulating bollworm herbivory, the cotton fiber yield in the final harvest will increase by 10%-30%. This kind of phenomenon that small damages are beneficial to plants themselves is called overcompensation, which has become a hot focus in ecology and evolution studies in recent years. Besides cotton, many scientists have also found a lot of other plants that have this characteristic, such as grass, tree and vegetable. The conditions required for producing overcompensation for a plant include developmental stage, sunlight, damage extent, damage sorts, etc. Our previous study has shown that 50% leaf removal from total canopy area, simulating insect herbivory, could increase boll number by 24.4 %. Furthermore, the peroxidase （POD） and polyphenol oxidase （PPO） activity were also changeable. This paper succeeds last experimental study of leaf removal, but we emphasized to observe the effect of larger extent of leaf removal on cotton growth and development and on the occurrence of overcompensation. Particularly, this paper studies chlorophyll and protective enzyme systems in cotton plants Gossypium hirsutum L. with 75 % and 100% leaf removal respectively, which belonged evidently to heavy leaf removal, of the total canopy leaf area at the early stage of primary anthesis. The results show that no overcompensation phenomenon with a higher cotton fiber yield produced in both cases of 75 % and 100 % leaf removal, whereas these cotton plants having obvious decreases in boll number of 5.4% and 9.8%, respectively. The new-born leaves on treated plants always presented larger area than that of control and the content of chlorophyll in these new-born leaves decreased during a short period. The level in chlorophyll content in leaves of 75% leaf removal and 100% leaf removal were 19.7% and 20.1% lower than that of control one week after leaf removal. In the meantime, the treatments for herbivory simulation of 75% leaf removal and 100% leaf removal decreased protein content in cotton leaves. One week after leaf removal, the protein content in 75 % leaf removal was 7.4% lower than that of control and 100% leaf removal was 23.1% lower than that of control. Importantly, heavy leaf removal made the highest point of protein content on protein curve appear one week later for the cotton plants with treatment of 75 % leaf removal and one more week later for the cotton plants with treatment of 100% leaf removal compared with control. The plants with large degree of leaf removal also had an enhanced activity of peroxidase （POD） but a. lowered activity of polyphenol oxidase （PPO） in new-born leaves. Two weeks after leaf removal, cotton leaves with 75% leaf removal had a POD activity 18.0% higher than control and 100% leaf removal had a POD activity 18.8% higher than control. Cotton leaves with 75% leaf removal had a PPO activity 7.0 % lower than control and 100 % leaf removal had a PPO activity 9.3 % lower than control one week after leaf removal. But the specific activity of both POD and PPO increased. All these experimental data suggest that heavy leaf removal not only wrecked the cotton plant homeostasis but also brought about cotton plant serious damage. The wrecked plants with small amount of proteins resulted from heavy leaf removal might be less resistant to other insect or non-insect infestations and could not recover easily from the damage so that they could correctly regulate their own metabolic machine going up onto the regular high level. The damaged homeostasis might have outaehieved the modulation limit of plant resistance and functional induction of transnormal ability. So, cotton plants with treatment of heavy leaf removal of 75% and 100% leaf removal at the early stage of primary anthesis could only give expressions of damage status. Together with the previous study, we conclude that if we want to get overeompenation on cotton plants from leaf loss, we should strictly confine the extent of leaf loss to no more than 75 % leaf removal. In agriculture, we can use this biological effect resulted from overeompensation to make certain methods to increase agricultural yield. Most crops are plants with high level of endurance for environmental stresses. If we positively make proper intensive artificial mechanical wounds as well as metabolic balance tissue or environmental stress, it is possible for us to get a good harvest without loss instead of those irregular insect and animal herbivory further utilization of fertilizer and plant hormones. In the meantime, the overcompensatory effect also implies an elevation upon concrete threshold of pest management, resulting in reducing the amount of insecticides and pesticides used for insect and pest management and saving the time for farmers. Large scale of application of pesticides in pest control often causes directly soil contamination and environmental air pollution, which severely influence our life quality. So tissue balance and small damage research to plants and animals have great importance to ecology. It seems that there could be chemical signals coming from homeostasis change in plants. These signals that might be small molecular substance, possibly in company with HSP protein, could move from damaged leaf tissues to the new-born leaves, after a long distance transport and transducing over petioles and stems, and regulate the activities of POD and PPO in new-born leaves. This signaling mechanism could be at least in part of the mechanism of overcompensation. If so, we will be thankful that ecology ultimately links to molecular biology. This finding may be interesting to some scientists in the field of molecular biology who have demonstrated that the ubiquitous protein chaperone hsp90 regulates more than 100 proteins involved in cellular signalling. But what factor directly enhances the specific activity of PPO like Ca^2＋ iron remains to be elucidated. This should be our next study direction of work.