A rapid increase in cytokinin levels and enhanced ethylene evolution precede Al3+-induced inhibition of root growth in bean seedlings (Phaseolus vulgaris L.)

Fruit sink strength or its ability to attract assimilates depends bothon sink activity and size. This study investigated one main component of sinksize, that is the number of fruit cells during tomato plant development. Plantswere grown in a controlled climate chamber under a limiting (LS, six fruits pertruss) and non-limiting (NLS, two fruits per truss and CO₂enrichment) supply of carbon assimilates. Under NLS conditions, fruit cellnumber was homogeneous among successive trusses, and fruits contained onaverage1.2×10⁶ more cells than under LS conditions,though differences were not significant on the first truss which underwent thelowest competition. Under LS conditions, an ontogenetic increase in cell numberwas observed in proximal fruits of the upper trusses attributed to theenlargement of the apical meristem during plant development. The decrease ofcell number from proximal to distal fruits within a truss, that was expectedfrom the literature, was generally observed in the LS experiment, with anaverage significant difference of about1.6×10⁶cells between the first and fifth fruits. Nevertheless, whereas the gradient incell number from proximal to distal fruits was steep in the upper trusses, itwas not significant on the lower trusses indicating that this gradient largelydepended on the level of competition during floral development. Thus, under lowassimilate supply, cell division is a main limiting factor for fruit growth,although cell enlargement during further fruit development is also affected,butwas not measured in this work.