Alka Srivastava

Hormonal Regulation of Tomato Fruit Development: A Molecular Perspective

Fruit development is a complex yet tightly regulated process. The developing fruit undergoes phases of cell division and expansion followed by numerous metabolic changes leading to ripening. Plant hormones are known to affect many aspects of fruit growth and development. In addition to the five classic hormones (auxins, gibberellins, cytokinins, abscisic acid and ethylene) a few other growth regulators that play roles in fruit development are now gaining recognition. Exogenous application of various hormones to different stages of developing fruits and endogenous quantifications have highlighted their importance during fruit development. Information acquired through biochemical, genetic and molecular studies is now beginning to reveal the possible mode of hormonal regulation of fruit development at molecular levels. In the present article, we have reviewed studies revealing hormonal control of fruit development using tomato as a model system with emphasis on molecular genetics.

Maturity and ripening-stage specific modulation of tomato (Solanum lycopersicum) fruit transcriptome.

Tomato (Solanum lycopersicum) fruit is a model to study molecular basis of fleshy fruit development and ripening. We profiled gene expression during fruit development (immature green and mature green fruit) and ripening (breaker stage onwards) program to obtain a global perspective of genes whose expression is modulated at each stage of fruit development and ripening. A custom made cDNA macroarray containing cDNAs representing various metabolic pathways, defense, signaling, transcription, transport, cell structure and cell wall related functions was developed and used to quantify changes in the abundance of different transcripts. About 34 % of 1066 unique expressed sequence tags (ESTs) printed on the macroarray were differentially expressed during tomato fruit ripening. Out of these, 25 % genes classify under metabolism and protein biosynthesis/degradation related processes, while a significant proportion represented stress-responsive genes and about 44 % represented genes with unknown functions. RNA gel blot analysis validated changes in a few representative genes. Although the mature green fruit was found transcriptionally quiescent, the K-means cluster analysis highlighted coordinated up or down regulation of genes during progressive ripening; emphasizing that ripening is a transcriptionally active process. Many stress-related genes were found up-regulated, suggesting their role in the fruit ripening program.

Biotechnological Interventions to Improve Plant Developmental Traits

Unprecedented progress during the last three decades in our understanding of the principles of a living cell, particularly the identification of genes and signaling pathways involved in cell differentiation and organ development, has brought us a broader insight into plant biological processes. Technological advancements are revealing new and fundamental knowledge at the molecular and cellular levels, knowledge that is critical towards achieving the goal of precision-based crop improvement. Modernday genetic engineering has emerged as a promising precision-based technology for boosting up food production in the world and introducing desirable traits such as nutritional enhancement and disease and pest resistance, both important components of agricultural sustainability (Chrispeels et al. 2002; Fatima et al. 2008; Negi and Handa 2008). Achieving results that benefit the world will depend on the success of applying new knowledge to real-world field scenarios. The challenge, therefore, is also to simultaneously obtain knowledge on agroecosystem structure and function to understand how manipulation and control of specific gene expression will translate into directing processes at the ecological scale (Mattoo and Teasdale 2009). Developmental traits are coordinated at various levels in a plant and involve organ-to-organ communications via long-distance signaling processes that integrate transcription, hormonal action and environmental cues. Thus, plant architecture, root–soil–microbe interactions, flowering, fruit (and seed) development, and fruit ripening (and seed germination) are highly regulated genetic programs that are also impacted by processes such as organ abscission, organ senescence (and ripening), and programmed cell death (PCD). We note that belowground processes provide the anchor for a healthy and robust plant (Mattoo and Teasdale 2009) but in this

Possible Evidence of Pre-Columbian Transoceanic Voyages Based on Conventional LSC and AMS 14C Dating of Associated Charcoal and a Carbonized Seed of Custard Apple (Annona squamosa L.)

An attempt was made to trace the antiquity of custard apple in India on the basis of accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) radiocarbon dates. Recently, seed remains of custard apple (Annona squamosa L.) in association with wood charcoals were encountered from the Neolithic archaeological site of Tokwa at the confluence of the Belan and Adwa rivers, Mirzapur District, in the Vidhyan Plateau region of north-central India. The wood charcoal sample was dated at the 14C laboratory of the Birbal Sahni Institute of Palaeobotany (BSIP), Lucknow, by conventional LSC 14C dating. The sample dated to 1740 cal BC (BS-2054). A seed sample of custard apple was dated by AMS at the Institute of Physics 14C laboratory, Bhubaneswar, India (3MV tandem Pelletron accelerator). Interestingly, the AMS date was given as 1520 cal BC (IOPAMS-10), showing a reasonable agreement with the LSC date carried out at BSIP. On botanical grounds, the custard apple is native to South America and the West Indies and was supposed to have been introduced in India by the Portuguese in the 16th century. The present 14C dates of the samples pushes back the antiquity of custard apple on Indian soil to the 2nd millennium BC, favoring a group of specialists proposing diverse arguments for Asian-American transoceanic contacts before the discovery of America by Columbus in AD 1492.