Studies On The Polar Transport And Distribution Of Auxin At Pegging Stage Of Peanut (Arachis Hypogaea L.)

Peanut(Arachis hypogaea L.)is the unique plant which produces flowers aerially, but buries the fertilized ovules into the soil, allowing fruit and seed development occur underground. The pegging stage is the critical period of transition from vegetative growth to reproductive growth, jointly regulated by several phytohormones.’Zhonghua4’ and ’Qiyangxiaozi’were used as the experimental materials. The content and distribution of plant hormones, the IAA distribution of transgenic peanut plants, the physiological changes of peanuts and microstructure of pegs were systematically studied in the pegging stage using14C isotopic tracer technique, DR5∷GFP genetic transformation technology, IAA and its inhibitor TIBA treatments, and the slant stimulus treatment. This research is aimed to realize the transport and distribution of auxin and the influencing factors of peanut at pegging stage, also as the references for the study of auxin transport and its role in pod development of plants.The main results are as follows:1. The IAA distributions and the effects of slant stimulus treatment on IAA distributions in different parts of peanut were analyzed during pegging stage. Results showed that IAA contents in roots were higher than in other organs. IAA contents were higher in peanut pegs at the25th day after flowering under the natural growth and slant stimulus treatment. IAA contents in roots and leaves were higher than the control after slant stimulus. IAA contents in stems were higher under slant stimulus treatment than the natural growth by84.87%and56.78%at the15th and25th days after flowering. While IAA contents in stems were significantly lower than the control by41.07%after the30d gravity stimulus. IAA contents in flowers were lower than the control with slant stimulus treatment. IAA content in the pegs had been reached the maximum after the20d slant stimulation. IAA contents in pegs after the20d and30d slant stimulations were lower than the pegs under the natural growth state by24.61%and7.81%respectively.2. The distributions of GA1, GA3and GA4and the effects of slant stimulus treatment on GA1, GA3and GA4distributions in different parts of peanut were analyzed during pegging stage. The results showed that the contents of GA1were significantly correlated with the contents of IAA in pegs and leaves. Highly significant and positive correlations were also found between IAA contents and the contents of GA1and GA3of flowers. GA1contents of pegs were higher than other organs at the25th day after flowering, but GA1contents of stems were very low. GA3contents were higher, especially in the25d after flowering, which had the similar tissue-specific character as GA1. The maximums of GA4were detected in stems, pegs and flowers respectively at different three sampling times. The redistributions of GAS were caused by slant stimulus.3. The transportation and distribution of14C-labelled auxin in different parts at the pegging stage of peanut have been revealed preliminarily. The results showed that the transport rate was approximately5mm·h-1downwards the stem when top leaves were treated. In case of root treatment,14C-IAA showed a transportation trend upwards. The accumulation of14C-IAA in roots was higher than in other parts, moreover the upwards transportation ability of14C-IAA was stronger at24h after the treatment. Whereas14C-IAA applied in the stem portions transported both upwards and downwards simultaneously, and14C-IAA content was found to be high in roots, stems and leaves at24h after treatment. The transportation of14C-IAA from flowers with pegs was found mainly downwards after being treated for72h. However the highest content of14C-IAA was found in leaves followed by stems and the lowest was in roots in case of14C-IAA transportation from flowers without pegs.4. The embryonic leaflets have been confirmed as the explants for tissue culture and Agrobacterium mediated genetic transformation, and the transformation system suitable for the embryonic leaflets was optimised. The integration of DR5∷GFP transgenes in the transformed plants were confirmed by PCR. It was found that the optimal conditions for higher transformation efficiency were as follows:one time infection treatment, the treatment time10min and co-cultivation for72h after preculture. The roots and pegs of transgenic plants with DR5∷GFP gene were observed by laser scanning confocal microscope, and the results showed that auxin in peanut root was mainly located the quiescent center of root and lower half of the lateral root cap, and most of the IAA signal occured in the epidermis, less in cortex of pegs.5. The effects of indole-3-acetic acid (IAA) and auxin polar transport inhibitor2,3,5-triiodobenzoic acid (TIBA) on IAA contents in different parts and the physiological changes of peanut were determined. Spraying10μM IAA at early flowering stage significantly stimulated IAA contents in different parts, the growth of stem and peg, the numbers of peg and flower, and the photosynthetic rate at pegging stage. Treatment with10μM TIB A at early flowering stage increased the first branch length and branch number per plant, while the stem height, peg length, peg number and flower number per plant were significantly inhibited. The average single pod weights of auxin and TIBA treatments were distinctly higher than the control by18.24%and6.76%respectively. The IAA contents of stems and leaves treated with10μM TIB A were also significantly increased. Pegging rate and net photosynthetic rate were enhanced, but the Ci was decreased than the control by8.06%under10μM TIBA treatment.6. The structures of peanut peg were similar to the overground stems of dicotyledonous herbaceous plants, which were epidermis, cortex, phloem, cambium, xylem and pith from outside to inside of peg by using scanning electron microscopy. Compared with the pegs under the natural state, the numbers of vascular bundles of pegs increased significantly, and the size of each vascular bundle was smaller after slant stimulus treatment. Meanwhile, the vascular bundles packed closely, had the sieve plate structrue, and the geotropic reaction was relatively insensitive under slant stimulus.