Physiological And Molecular Basis On Resistance To Iron Chlorosis In Malus Xiaojinensis And Citrus Junos

IntroductionIron chlorosis of food crop plants and fruit trees grown on alkaline, or calcareous soils is a widespread agricultural problem in the world. Although abundant in these soils, iron is often insoluble and therefore is unavailable for the plants roots. Statistics show that potential iron-deficiency exists in plants growing in 25%~30% soils of the globe. Iron deficiency causes interveinal chlorosis, mesophyll yellowing or paling and leaf size reduction and, if severe enough, retards the growth of the plants and may even cause their death, thus resulting in great losses to agricultural production. Fruit trees are very important economic crops in people's life, the losses of fruit production caused by iron chlorosis are usually higher than those of other annual economic crops because fruit tress, as perennial plants, will remain there for many years after they are planted in a field and an evident accumulation effect may take place. Unfortunately, the widespread problem of iron chlorosis of fruit trees remains poorly understood and the results of the methods for its correction are not satisfactory, and they sometimes cause serious environmental problems as well. With the advances in molecular biology and modern biological engineering technology, scientists begin to look for new ways to tackle this problem. It has become possible to create new iron efficient plant materials or to avoid soil environmental pollution by creating new rootstocks with high iron efficiency as well as excellent complex characters. C. junos and M. xiaojinensis were found to be tolerant to iron chlorosis and were able to acquire iron from soils of low iron availability in previous field experiments, but the physiologicaland molecular mechanisms for their iron efficiency have remained unclear. The purposes of this project were to further analyze the characteristics of their iron efficiency under iron stress, to study the physiological and molecular mechanisms of iron efficiency under iron deficiency in C. junos and M. xiaojinensis , and to analyze the spatial expression model of FCR (ferric chelate reductase) gene under iron stress with the hope to cast a new light on iron stress tolerance on the molecular level, to lay solid foundations for cloning FCR gene in C. junos and M. xiaojinensis, and to provide some basic data for creating new rootstocks with excellent complex characters and iron efficiency. The main results are presented as follows: 1. The physiological reaction of C. junos under iron stressIn field experiments, C. junos manifested itself as tolerant to iron stress. No chlorosis symptom was not found in its leaves when it was grown in a soil with pH 7.8. In contrast, severe chlorosis was found in the control plant P. trifoliata grown under the same soil conditions, and leaf chlorophyll content as an indicator for the degree of Fe deficiency in P. trifoliata was much lower than in C. junos. In solution culture, evident chlorosis symptoms were observed in the leaves of P. trifoliata after 4 weeks of iron deficiency treatment, while no chlorosis symptoms were observed in the leaves of "iron efficient" C. junos under the same culture conditions. The content of leaf chlorophyll and active iron in C. junos was much higher than that of P. trifoliata. However, iron content of chlorotic leaves of P. trifoliata was found to be even higher than that of the green leaves of P. trifoliata and C. junos. Just as reported before, Fe is only case where its content in plant tissues is not correlated with the degree of its deficiency.Net H excretion in C. junos was rapidly activated by iron deficiency and its rate was enhanced 4 days after the start of the treatment as compared with the non-deficiency control, and this trend lasted over 12 weeks under iron deficiency. In P. trifoliate, net H+ excretion rate was also enhanced under 4 days' iron deficiency, but was no longer observed under iron deficiency for 12 weeks. NOs-N was used as the N source of the culture solution and it increased pH of solution. The extent of the increa...