Characterization of <Emphasis Type="Italic">GA20ox</Emphasis> genes in tall and dwarf types coconut (<Emphasis Type="Italic">Cocos nucifera</Emphasis> L.)

Coconuts (Cocos nucifera L.) are divided by the height into tall and dwarf types. In many plants the short phenotype was emerged by mutation of the GA20ox gene encoding the enzyme involved in gibberellin (GA) biosynthesis. Two CnGA20ox genes, CnGA20ox1 and CnGA20ox2, were cloned from tall and dwarf types coconut. The sequences, gene structures and expressions were compared. The structure of each gene comprised three exons and two introns. The CnGA20ox1 and CnGA20ox2 genes consisted of the coding region of 1110 and 1131 bp, encoding proteins of 369 and 376 amino acids, respectively. Their amino acid sequences are highly homologous to GA20ox1 and GA20ox2 genes of Elaeis guineensis, but only 57% homologous to each other. However, the characteristic amino acids two histidines and one aspartic acid which are the two iron (Fe²⁺) binding residues, and arginine and serine which are the substrate binding residues of the dioxygenase enzyme in the 20G-FeII_Oxy domain involved in GA biosynthesis, were found in the active site of both enzymes. The evolutionary relationship of their proteins revealed three clusters in vascular plants, with two subgroups in dicots and three subgroups in monocots. This result confirmed that CnGA20ox was present as multi-copy genes, and at least two groups CnGA20ox1 and CnGA20ox2 were found in coconut. The nucleotide sequences of CnGA20ox1 gene in both coconut types were identical but its expression was about three folds higher in the leaves of tall coconut than in those of dwarf type which was in good agreement with their height. In contrast, the nucleotide sequences of CnGA20ox2 gene in the two coconut types were different, but the expression of CnGA20ox2 gene could not be detected in either coconut type. The promoter region of CnGA20ox1 gene was cloned, and the core promoter sequences and various cis-elements were found. The CnGA20ox1 gene should be responsible for the height in coconut, which is different from other plants because no mutation was present in CnGA20ox1 gene of dwarf type coconut.     

Screening sugarcane (Saccharum sp.) genotypes for salt tolerance using multivariate cluster analysis

Disease-free sugarcane plantlets of 11 cultivars derived from meristem cuttings were photoautotrophically grown on the MS medium and subsequently exposed to 0 (control) or 200?mM NaCl (salt stress) for 14?days. Sodium ion (Na⁺) in all sugarcane varieties was enriched when plantlets were subjected to 200?mM NaCl, except K88-1. Chlorophyll a (Chl_a), chlorophyll b (Chl_b) and total carotenoids (C_x+c), in the salt stressed leaves of all genotypes decreased significantly, but the extent of decrease was variable among different genotypes. In contrast, proline content in salt stressed plantlets of all sugarcane genotypes increased markedly, except in genotypes K95, K92-2 and LK92-4. Maximum quantum yield of PSII (F_v/F_m), photon yield of PSII (??_PSII), quantum efficiency of PSII (qP) and net photosynthetic rate (P_n) in salt stressed plantlets of all genotypes were significantly dropped, whereas ??_PSII and qP in cv. KK88-1 were alleviated, resulting in improved P_n. Moreover, growth parameters including shoot height, root length, fresh weight, dry weight and leaf area in salt stressed plantlets of all genotypes were significantly inhibited. The Na⁺ accumulation, pigment degradation, proline accumulation, photosynthetic abilities and growth inhibition in saline regimes were subjected to Hierarchical cluster analysis. Salt tolerant, K88-1 and UT94-7 and salt susceptible, K92-2 and LK92-4 classes of sugarcane genotypes were classified. The salt tolerant cultivars may be further studied including yield, sugar content and ratoon recovery rate in saline field trials.