The tomato mutant ars1 (altered response to salt stress 1) identifies an R1-type MYB transcription factor involved in stomatal closure under salt acclimation.

A screening under salt stress conditions of a T-DNA mutant collection of tomato (Solanum lycopersicum L.) led to the identification of the altered response to salt stress 1 (ars1) mutant, which showed a salt-sensitive phenotype. Genetic analysis of the ars1 mutation revealed that a single T-DNA insertion in the ARS1 gene was responsible of the mutant phenotype. ARS1 coded for an R1-MYB type transcription factor and its expression was induced by salinity in leaves. The mutant reduced fruit yield under salt acclimation while in the absence of stress the disruption of ARS1 did not affect this agronomic trait. The stomatal behaviour of ars1 mutant leaves induced higher Na(+) accumulation via the transpiration stream, as the decreases of stomatal conductance and transpiration rate induced by salt stress were markedly lower in the mutant plants. Moreover, the mutation affected stomatal closure in a response mediated by abscisic acid (ABA). The characterization of tomato transgenic lines silencing and overexpressing ARS1 corroborates the role of the gene in regulating the water loss via transpiration under salinity. Together, our results show that ARS1 tomato gene contributes to reduce transpirational water loss under salt stress. Finally, this gene could be interesting for tomato molecular breeding, because its manipulation could lead to improved stress tolerance without yield penalty under optimal culture conditions.

Genetic analysis of reproductive development in tomato.

Besides being an important commercial crop, tomato (Solanum lycopersicum L.) constitutes a model species for the study of plant developmental processes. Current research tends to combine classic disciplines such as physiology and genetics with modern approaches coming from molecular biology and genomics with a view to elucidating the biological mechanisms underlying plant architecture, floral transition and development of flowers and fruits. Comparative and functional analyses of tomato regulatory genes such as LATERAL SUPPRESSOR (LS), SELF PRUNING (SP), SINGLE FLOWER TRUSS (SFT) and FALSIFLORA (FA) have revealed mechanisms involved in shoot development and flowering time which are conserved among Arabidopsis, tomato and other plant species. Furthermore, several regulatory genes encoding transcription factors have been characterized as responsible for singular features of vegetative and reproductive development of tomato. Thus, the sympodial growth habit seems to require a specific control of the developmental fate followed by shoot meristems. In this process, novel genetic and molecular interactions involving SP, SFT and FA genes would be essential. Also this latter, but mainly ANANTHA (AN) and COMPOUND INFLORESCENCE (S) have recently been found to regulate the inflorescence architecture of the tomato. Concerning fruit development, genetic and molecular analyses of new genes such as fw2.2, FASCIATED, OVATE and SUN have proved their contribution to the domestication process and most importantly, their function as key regulators of fruit size and shape variation. Tomato ripening is also being elucidated thanks to the characterization of regulatory genes such as RIPENING INHIBITOR (RIN), NON-RIPENING (NOR), TDR4 and COLORLESS NON-RIPENING (CNR), which have been found to control early stages of fruit development and maturation. At the same time, much research is dedicated to isolating the targets of the ripening regulators, as well as the key genes promoting the parthenocarpic development of tomato fruits. Hopefully, the ongoing sequencing project and the progress made by integrating several research fields will help to unravel the genetic and molecular pathways controlling tomato development.

Development of a novel casein-protamine based microparticles for early feeding of fish larvae: in vitro evaluation.

OBJECTIVE: The objective of this study was to develop novel type of protein walled microparticles suitable for using in early feeding of fish larvae. METHODS: The microparticles were made of casein and protamine through complex coacervation and did not require further cross-linking or use of environmentally problematic reagents. The methodology was oriented to generate microparticles with an appropriate size range for easy recognition and ingestion by fish larvae (50-200 microm), adequate floating properties in saline, sufficient stability in terms of protein leakage and appropriate digestibility by the gut enzymes of fish larvae. RESULTS: Desired particle size and stability against protein leakages over 8 h were successfully achieved by optimizing the coacervation process conditions. The floating properties under static conditions were considered appropriate as a main particle fraction remained in suspension during at least 10 min. Very importantly, an enzyme extract from larval gut readily digested the particles. The digestibility of the casein-protamine particles was similar to that measured for Artemia nauplii and for two previously developed casein-based microparticles produced by interfacial polymerization and ionic gelation; the latter microparticle type had previously achieved good results of digestibility in early feeding of marine fish larvae. CONCLUSION: The in vitro evaluation of the newly developed casein-protamine microparticles revealed promising characteristics as artificial larval feed. Thus, these particles merit further development with respect to entrapping nutrients and testing them in larval cultures for their nutritional value.