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Falling fruit or filling fruit
‘Just look at the fruit on that!’ exclaimed my companion, a distinguished plant physiologist for whom the internal transport logistics of plants holds a strong fascination. At the time, we were looking at a date palm and the point he went on to make was that a large amount of material is needed to be transported over relatively long distances for the fruit to grow to maturity. Just this problem has been investigated by García-Luis et al. at Valencia (pp. 755-764) but working with clementines (Citrus clementina) rather than with dates. In this species, a significant proportion of the ovaries are shed after anthesis but before fruit set. Later, abscission of fruitlets takes place, and by fruit maturity only a small proportion of the original flowers (7 % in this instance) are retained as fruit. Pedicel vascularization occurs early in fruit growth and the phloem reaches its maximum cross-sectional area at the end of the main fruitlet abscission phase. Xylem continues to expand and to undergo thickening rather longer, concomitant with the need for increasing support as the fruit enlarge. Then come the key questions: are either the fate of the fruit (abscission or maturation) or the rate of dry matter accumulation in maturing fruit limited by the phloem in the pedicel? Dealing with the second question, removal of 37 % of the phloem by girdling increased the specific mass transfer in the remaining phloem but caused no decrease in fruit growth rate. Thus, the phloem responded to the growth pattern of the fruit rather than the reverse. In respect of the first question, the authors state in their discussion that the ‘fate of developing fruitlets is determined early in their development’ and indeed may already be determined at the time of flowering, an intriguing statement that clearly calls out for more research!
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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