SOURCE-SINK RELATIONSHIP AND PROTEA POSTHARVEST LEAF BLACKENING

The inflorescence of Protea neriifolia B. Br. was two-thirds of the to tal cut floral stem fresh weight and significantly influenced blackeni ng of the attached 20 to 30 leaves. Floral stems harvested at five dev elopmental stages were characterized for inflorescence diameter, fresh and dry weights, respiration, and nectar production. Inflorescence di ameter and fresh and dry weights increased from stage 1 (very tight bu d) to stage 5 (bracts reflexed). Respiration rate was high in stages 1 and 3, Nectar production began at stage 4 (open, cylindrical flower) and increased from 2.7 to 9.8 ml per flower with 15% to 23.5 % total s oluble solids as the flower opened. Postharvest inflorescence diameter , respiration rate, and nectar production increased and leaf blackenin g decreased when floral stems were plated in 5% (w/v) sucrose solution . Application of C-14-sucrose to a leaf subtending the inflorescence l ead to >50 % of the radioactivity being found in the nectar within 24 hours. These data indicate that leaf blackening in protea is the resul t of depletion of carbohydrate by the inflorescence, and that this dep letion is primarily due to the sugar demand for nectar production.