Our observations, performed at five time points during the period from fruit set through the end of exponential fruit growth, indicate that this is a dynamic period of cucumber fruit development involving an array of internal and external morphological, physiological, and transcrip tomic changes that act in concert with phases of active cell division, expansion, and response to the environ ment. Relative to anthesis and early fruit set, the period of peak and late exponential growth includes a large portion of highly represented transcripts, either of unknown function, or without homologs in Arabi dopsis, suggesting unique factors contributing to the rapid growth phase in cucurbits.
The end of exponen tial growth was marked by a shift in transcriptome profile characterized by abiotic and biotic stress related genes and significant enrichment for transcription factor gene homologs associated with stress response and development, suggesting that the interval between expansive growth and ripening selleck chemicals may include a pro grammed transition toward enhanced defense. Results and discussion Morphological changes during early cucumber fruit development Young Vlaspik cucumber fruit followed a highly repro ducible progression of growth and development includ ing visible external and internal morphological changes. Increase in size occurred rapidly after fertilization with most rapid growth occurring between 4 and 12 dpp. After approximately 16 dpp, fruit size remained largely constant until fruit maturation at ap proximately 30 dpp. At 0 dpp, deep ridges along the length of fruit covered the surface of the fruit.
Densely spaced spines were randomly selleck chemical scattered relative to the ridges. In contrast to ridges, which were most prominent at anthesis, warts, which are typic ally are formed at the base of spines, were diminutive at 0 dpp. They rapidly developed to become highly promin ent at 4 dpp but then flattened out with further fruit ex pansion. Both ridges and warts were nearly absent by 12 dpp. The spines followed a maturation process culminat ing in abscission. At 0 dpp spine color was translucent light green. At approximately 8 dpp they started to sen esce, turning yellow, then white at 1216 dpp. By 16 dpp many had abscised from the fruit surface. At anthesis, the exocarp was dark green. Dark green light green stripes and specks on the surface of the fruit began to emerge around 8 dpp.
The fruit surface at an thesis also has a dull appearance due to bloom, a fine white powder primarily composed of silica oxide. The bloom disappeared first from the peduncle end around 4 dpp, then the blossom end by 8 dpp. by 12 dpp, it had disappeared completely, leaving a shiny fruit surface. The cuticle layer showed increased thickness with age. After 12 and 16 dpp it stained more darkly with Sudan IV, indicating increased cutin or wax content that appeared to penetrate between the pallisade cells in the epidermal layer.