Organogenesis fromSolanum melongena L. (eggplant) cotyledon expiants is associated with hormone-modulated enhancement of polyamine biosynthesis and conjugation

Abstract

Summary. Eggplant (Solanum melongena L. cv. Violetta lunga 2)cotyledon explants grown on hormone-free medium (controls) or on medium containing either naphthaleneacetic acid alone (root forming) or in combination with zeatin riboside (shoot forming) showed minor differences in free polyamine titres during culture. In contrast, conjugated polyamines (particularly those in the trichloroacetic acid-soluble fraction) accumulated only in hormonetreated explants, but not in controls. The extent and the temporal changes in soluble-conjugate levels differed between root-forming and shoot-forming explants; in the former, accumulation began earlier (within 1 day of culture) and reached the highest levels. In both organogenic programmes, maximum conjugate accumulation occurred just before and during organ emergence. Adventitious roots and shoots were formed along the cut surfaces. The regions closest to these ("borders") displayed a significantly higher ratio of conjugated to free spermidine and/or putrescine than the nonorganogenic regions ("centres") of the explant. Ornithine decarboxylase activity was higher than arginine decarboxylase activity both in control and hormone-treated explants. However, both activities increased markedly on day 2 of culture in the presence of hormones. Thereafter ornithine decarboxylase activity remained high in shoot-forming explants, but not in root-forming ones. Putrescine oxidising activity was also enhanced by exogenously supplied hormones starting from day 4 of culture. This activity remained high up to day 12 in the presence of auxin plus cytokinin, whereas it peaked on day 6 in auxin-treated explants. Spermidine oxidising activity was the only enzyme activity which was consistently higher in controls than in hormone-treated tissue. Differences between the two organogenic programmes with respect to temporal changes in polyamine content, and putrescine biosynthetic and oxidative activities are discussed in relation to the timing of organ formation. The latter was monitored both histologically and macroscopically. Abbreviations: PA polyamine; Put putrescine; Spd spermidine; Spm spermine; NAA naphthaleneacetic acid; ZR zeatin riboside; TCA trichloroacetic acid; ODC ornithine decarboxylase; ADC arginine decarboxylase.

Effect of Genotype, Explant and Hormonal Concentration on in Vitro Response of Eggplant

“…Though the explant biochemical or molecular basis of such differential response as a function of culture time could not be ascertained from the present study, it may be conjectured from the information available from earlier works that endogenous hormonal levels as well as those of polyamines might be changing with culture time and may influence the final response (Fobert and Webb, 1988;Sharma and Rajam, 1995;Momiyamma et al, 1995;Rajam, 1997, 1998;Scoccianti et al, 2000). The present accessions and explant types might provide suitable experimental system to undertake detailed analysis of these biochemical factors.…”

“…In S. melongena, regeneration from the cotyledonary explants at different developmental stages ranging from one week old to 30 days old have been reported (Alicchio et al, 1982;Fobert and Webb, 1988;Rao, 1992;Saito and Nishimura, 1994;Momiyama et al, 1995;Sharma and Rajam, 1995;Hitomi et al, 1998;Magioli et al, 1998;Scoccianti et al, 2000;Tarre et al, 2004;Rahaman et al, 2006). Rama Swami et al (2005) reported in vitro response of cotyledons from three week old seedlings of S. surattense.…”

Indirect Shoot Organogenesis of Eggplant (Solanum Melongena L.)

“…Also, callus induction response may be affected by the specificity of explants used for shoot regeneration; thus, explants from 30-days old seedlings revealed better callus induction frequency and subsequent regeneration compared with explants from in vitro developed older plants. Further, the differences in callus and organ induction may be a result of genotype or cultural conditions (Franklin et al, 2004;Magioli et al, 1998;Mir et al, 2008;Scoccianti et al, 2000;Sharma, Rajam, 1995). In our case, duration of callus proliferation on cultural media was very important for shoot regeneration.…”

Eggplant (Solanum melongena L.): tissue culture, genetic transformation and use as an alternative model plant

“…Different plant in vitro morphogenic systems have been used to study the role of polyamines (PA), which are proposed as a new class of growth regulators involved in differentiation, reproduction, disease resistance and stress (Scoccianti et al 2000). Eggplant tissues may favour a clearer picture of these molecular signals in differentiation processes, considering their ability to regenerate plants in vitro through different morphogenetic processes.…”