مقایسه برخی‌ از پاسخ‌های رشدی، بیوشیمیایی و هورمونی سرشاخه‌های گال‌دار دو گونه از درختان بید

جارویی شدن سرشاخه های درختان بید (معمولی و مجنون)، توسط فیتوپلاسما ایجاد شده و با تغییر شکل قابل توجه در آن ها بروز می کند. پژوهش حاضر برای بررسی تغییرات رشد، قندهای محلول کل، کلروفیل کل، فعالیت آنزیم‌های آسکوربات پراکسیداز و پلی فنل اکسیداز و میزان هورمون ها (اکسین، جیبرلین و سیتوکینین) برگ های سرشاخه های گال دار در مقایسه با برگ های سالم انجام شد. جهت اجرای این پژوهش، در اواخر فصل بهار، از برگ های سرشاخه های گال دار و سالم درختان بید معمولی و مجنون پارک ناژوان، شهر اصفهان به صورت تصادفی نمونه برداری شد. نتایج نشان دادند صفات رویشی، کلروفیل کل و قندهای محلول سرشاخه های گال دار هر دو گونه ی بید، نسبت به سرشاخه های سالم مجاور کاهش معنی دار داشتند، ولی میزان محتوای نسبی آب و فعالیت آنزیم پلی فنل اکسیداز در برگ های سرشاخه های گال دار در هر دو گونه درخت بید مشابه برگ های سالم بود. برخلاف عدم تغییر معنی دار فعالیت آنزیم آسکوربات‌پراکسیداز در بید مجنون، میزان فعالیت آن در سرشاخه های گال دار بید معمولی کاهش یافت. میزان هورمون سیتوکینین در سرشاخه های گال دار هر دو گونه بید، بیش از 50 درصد افزایش داشت، امّا میزان هورمون اکسین و جیبرلین در سرشاخه های گال دار بید معمولی و مجنون نسبت به برگ های سالم مجاورشان به ترتیب 30.6 و 33.6 درصد کاهش یافت. کاهش رشد به همراه عدم تغییر محتوای نسبی آب برگ های جارویی شده هر دو گونه از درختان بید که با تغییرات هورمونی خاص آن گونه همراه شده سبب ایجاد ساختار منحصر به فرد گال آن گونه شده است.

comparative of some growth, biochemical, and hormonal responses of galled branches of two species of willow trees

the witches’ broom of the willow trees is induced by photoplasma in the galled branches. the aim of the study is the evaluate the changes in growth and physiological factors and the plant growth-promoting hormones (auxin, gibberellin, and cytokinin) in leaf witches’ broom branches compared with those healthy symptomless branches. the samples were collected from the leaves of ungalled and galled branches of both willow trees in najvan park, isfahan. results showed that growth parameters, total chlorophyll, and total soluble carbohydrates were decreased in the leaves of witches’ broom branches in both species. however, the relative water content and polyphenol oxidase activity did not show a significant change as compared with those of ungalled branches. in contrast, the ascorbate peroxidase activity did not show a significant difference between the leaves of ungalled and witches’ broom branches in s. babylonica, but its activity was decreased in witches’ broom branches of s. alba. the cytokinin content was increased (more than 50%) in the leaves of witches’ broom branches of both species, but the auxin and ga3 contents in the leaves of witches’ broom branches of s. alba and s. babylonica were significantly decreased by 30.6% and 33.6% respectively as compared with those of healthy control leaves. the concentration of total chlorophyll and water-soluble sugar decreased due to oxidative stress induced by phytoplasma. reduced growth with no significant change in the relative water content of galled branches in both willow trees is accompanied by the specific hormonal changes of each species which is formed of specific galls for each species.  introductionthe genus willows (salix) are shrubs and trees that usually grow in most parts of the earth. plant galls are neoformed organs that develop under the influence of galling organisms. insects, nematodes, viruses, bacteria, mycoplasma, fungi, other plants, and mites are typically considered gall inducers. they cause structural and metabolic changes in their host plants, leading to the formation of the gall organ. three hypotheses nutrition, microenvironment, and enemy have been proposed for forming galls by insects. the gall formation depends on the level of gene transcription interactions that exist between gall inducers and plants. the function of these genes causes changes in growth and development processes, cytoskeleton organization, cell walls, metabolic pathways, and plant hormone pathways. recently, candidatus phytoplasma trifolii caused willow catkin gall on salix babylonica and s. alba trees, characterized by a unique case of neoplastic formation like witches’ broom structure. the aim of the study is the evaluate of the changes in growth and physiological factors and the plant growth-promoting hormones (auxin, gibberellin, and cytokinin) in leaf witches’ broom branches compared with those healthy symptomless branches. material and methodsleaf samples of trees with gall and their symptomless adjacent branches were collected from najvan park, isfahan province, iran. the length and width of the leaves were measured and recorded. fresh and dry weights and relative water content (rwc) of leaves were measured. total chlorophyll was measured according to the arnon assay. water soluble carbohydrates were assessed using the method of dubois et al. (1956). activities of ascorbate peroxidase (apx) and polyphenol oxidase (ppo) were measured by the methods of asada and takahashi (1987) and kar & mishra (1976), respectively. high-performance liquid chromatography (hplc) was used to analyze plant growth-promoting hormones. results and discussionthe gall formation in salix species is caused by candidatus phytoplasma trifolii. the gall formation was accompanied by a reduction in the growth of leaves and shoots, which was represented by smaller leaves and shorter internodes. the gallers used nutritional resources of gall and adverse effects on the growth and survival of the host plants. results showed that relative water content (rwc) showed no significant changes between the witches’ broom structure compared with those of healthy control leaves in both salix species. reduction in growth without change in rwc is due to the modification in the expression of genes which is indicated by smaller leaves in gall. total chlorophyll was reduced in all gall-infected tissue of both salix species. the reactive oxygen species (ros) generated to respond to the biological stress in chloroplast can induce oxidative damage to the photosynthetic pigments which leads to the reduction of soluble sugars in the galled leaves. polyphenol oxidase (ppo) activity did not show a significant change as compared with those of healthy branches in both galled leaves salix species. in contrast, the ascorbate peroxidase activity did not show a significant difference between the leaves of ungalled and galled branches in s. babylonica. however, its activity was decreased in galled branches of s. alba, which indicated the activity of these enzymes is not a priority in both galled leaves salix species. the cytokinin content was increased in the leaves of witches’ broom branches of both species. however, the auxin and ga3 contents in the leaves of witches’ broom branches of s. alba and s. babylonica were significantly decreased by 30.6% and 33.6% respectively as compared with those of healthy control leaves. enhanced cytokinin content in both willow species can be introduced as the main factor in increasing the divisions of witches’ broom branches, which is coordinated with the particular hormonal changes each species which generates special galls them.  conclusionscandidatus phytoplasma trifolii reduced the growth of infected tissues characterized by smaller leaves and shorter internodes, followed by the formation of gall structure in both salix species. according to the results, the high accumulation of ros in response to the gall formation was accompanied by a reduction of total chlorophyll and water-soluble carbohydrates. altogether, it seems that the adverse effects of gallers on salix species refer partly to oxidative stress, which is synchronized with the specific hormonal changes of each species. these events cause the creation of special galls for each species.