Studies On The Mechanism Involved In Adaptive Responses Of Lateral Roots Growth To Phosphorus-deficiency Stress In Rice(Oryza Sativa L.)

Six rice (Oryza sativa L.) genotypes with different performances under P deficiency stress were tested in mixed growth medium of vermiculite and sand under different P supply conditions to evaluate the effects of P deficiency stress on lateral root growth and the relations between P deficiency induced lateral root growth and P absorption. The results showed that elongation and development of lateral root were induced by P deficiency. There was significant genotypic variation in lateral root growth in response to P deficiency. A significant positive correlation was observed between the increase of LRLP and the increase of RSAP, while no significant correlation was observed between the increase of LRNP and the increase of RSAP. The result suggested that the increase of root surface area under P deficiency condition could be mainly attributable to the increase of lateral root length induced. P uptake was significantly positively correlated with the total root surface area and positively correlated with the total lateral root length and the total lateral root number under P deficiency condition, which implied that elongation and development of lateral root were important to P uptake ability in growth medium where P supply was deficient. Soluble sugar content analysis indicated that P deficiency stress change the distribution of carbohydrate between roots and shoots.To understand the mechanism of lateral root growth induced by P deficiency, Six cDNA clones related to root growth were used as probes to hybrid with total RNA extracted from rice seedling treated with P starvation stress. Its expression pattern were summaried as folio wings:1) The expression of two Cyclin-Dependent Kinases(CDKs) genes in rice, cdc2Os-l and cdc2Os-2 were mainly localized in root, while only weak signal was detectable in leaf. Moreover, the higher cdc2Os-l expression was detected in P starvation -treated root than untreated root, while cdc2Os-2 transcript in root was pooly or not induced at all in response to P starvation. However, almost no cdc2Os-3 and R2 transcripts can de detected in root and leaf. According to these results, it was proposed that P starvation induced the expression of CDK gene cdc2Os-l and subsequently promoted the division of meristematic cells in root, thereby speeded up the elongation of adventitious root in rice.The increase of adventitious root growth may play a important role in P uptake under P starvation stress.The cdc2Os-l showed polymorphism between IR64 and Azucena, and was mapped on chromosome 3 using the molecular map of a DH population derived from a cross between IR64 and Azucena. The cdc2Os-l was linked to a RFLP maker, RG104.2) Two MADS-BOX genes, ANR1 and OS-MADS-1 both weakly expressed in root and leaf of rice, and were not induced by P starvation stress. The result suggested the mechanism of the increase of lateral root growth induced by P starvation was different from the mechanism of the increase of lateral root growth induced by low concentration of NOs" as signal.3) As a functionally unknown gene specifically involved in the initiation and development of lateral root primordia, the expression of LRP1 (Lateral Root Primordia 1, LRP1) was strongly blocked by P starvation, also by N starvation. The results indicated the initiation and development of lateral root were influenced by the availability of nutrient.4) NAC1, a new member of the NACs family, showed a increased transcript level in P starvation-treated root, suggesting P starvation induced its expression. The result supported that NAC1 was induced by auxin and mediated auxin signaling to promote lateral root development. It was proposed NAC1 was involved in the regulation of the initiation and development of lateral root induced by P starvation stress.