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Source-sink Relationship During Papaya Fruit Development and Ripening
|Title:||Source-sink Relationship During Papaya Fruit Development and Ripening|
|Abstract:||The source sink relationship during papaya fruit development and ripening was investigated. The source size and sink strength were modified by single or continual defoliation, and fruit thinning, respectively. The relationship between fruit growth, respiration, sugar accumulation and the activity of sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase were determined in fruit from 14 days after anthesis (DAA) to 140 DAA (harvest maturity) and in response to defoliation and fruit removal. A putative complete invertase gene and a SS gene fragment were isolated and characterized from nearly mature green papaya fruit. Single defoliation significantly reduced new flower and fruit set, and ripe fruit total soluble solids (TSS) but did not reduce fruit production, average fruit mass, percentage fruit flesh and seed, seed mass ratio and seed dry mass during a six weeks period. Continual defoliation in addition reduced fruit size, sugar and invertase enzyme activity and fruit production. The responses of defoliation and fruit thinning varied between different cultivars, weather conditions, defoliation time, degree and method. The pattern of gene expression during fruit development was compared with invertase extracted enzyme activity in the presence and absence of sodium chloride (NaCI) and by western blot analysis. The papaya invertase sequence had an open reading frame that encoded a polypeptide chain of 582 residues and calculated molecular weight of 65, 684 Da. The protein was highly homologous to known plant cell wall invertase and 67% identical at the amino acid level to carrot cell wall invertase. The cloned 720 bp SS fragment was highly homologous to A. glutinosa (X92378) and SS genes from other species. Invertase gene was expressed at a higher level during late fruit development stage than in young fruit and other tissues of papaya plant. SS gene expression was higher in young fruit and petiole tissues than in other tissues. The data demonstrated that SS enzyme was a major enzyme in fruit sink establishment and maintenance. Apoplastic invertase had an important function in phloem unloading during papaya fruit sugar accumulation and the activity was regulated at both transcriptional and translational levels.|
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Ph.D. - Horticulture|
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