Retranslocation of carbon reserves from the woody storage tissues into the fruit as a response to defoliation stress during the ripening period in Vitis vinifera L.

Abstract

Abstract.A technique for reliable labeling of the carbon reserves of the trunk and roots without labeling the current year's growth of grapevines was developed in order to study retranslocation of carbon from the perennial storage tissues into the fruit in response to defoliation stress during the ripening period. A special training system with two shoots was used: the lower one (feeding shoot) was cut back and defoliated to one single leaf (14CO2-feeding leaf)while the other (main shoot) was topped to 12 leaves. The potted plants were placed in a water bath at 30~ to increase root temperature and therefore their sink activity. Additionally, a cold barrier (2-4~ was installed at the base of the main shoot to inhibit acropetal 14C translocation. Using this method, we were able to direct labeled assimilates to trunk and roots in preference to the current year's growth. On vines with root and shoot at ambient temperature, 44% of the 14C activity was found in the main shoot 16 h after feeding whereas only 2% was found in the temperature-treated vines. At the onset of fruit ripening, and at three-week intervals thereafter until harvest, potted grapevines were fed with 14CO2 using the temperature treatment described above. Sixteen hours after feeding, half of the vines of each group were defoliated by removing all except the two uppermost main leaves. Three weeks after each treatment, vines were destructively harvested and the dry weight and 14C incorporation determined for all plant parts. Under non-stressing conditions, there was no retranslocation of carbon reserves to support fruit maturation. Vines responded to defoliation stress by altering the natural translocation pattern and directing carbon stored in the lower parts to the fruit. In the three weeks following veraison (the inception of ripening in the grape berry), 12% of the labeled carbon reserves was translo- cated to the fruit of defoliated plants compared to 1.6% found in the clusters of control vines. Retranslocation from trunk and roots was highest during the middle of the ripening period, when 32% of the labeled carbon was found in the fruit compared to 0.7% in control plants. Defoliation during this period also caused major changes in dry-matter partitioning: the fruit represented 31% of total plant biomass compared to 21% measured in the control vines. Root growth was reduced by defoliation at veraison and during the ripening period. Defoliation three weeks before harvest did not affect dry matter or 14C partitioning.

Net carbon exchange in grapevine canopies responds rapidly to timing and extent of regulated deficit irrigation

“…There have been mixed observations on the movement of labelled carbon from leaves to trunks, which could be reduced under severe water stress, although perhaps not under moderate water stress (Bota et al 2004). Roots reportedly are a low priority sink for carbon during fruit ripening (Candolfi-Vasconcelos et al 1994), but measurements of fine root length density in our companion study (Schreiner et al 2007) appear to contradict that notion because regardless of RDI regimen, fine root length density increased over time with a maximum value at harvest. Nonetheless, there was less total production of fine roots in RDI E vines because the timing of the additional deficit resulted in the greatest cumulative reduction in NCE C and because the additional deficit was imposed when roots were growing most rapidly.…”

Within-season temporal variation in correlations between vineyard canopy and winegrape composition and yield

“…The lack of consistency in correlations and the generally low magnitude of those significant correlations (Tables 4, 5) suggest that TSS concentration in harvested fruit has a more complex relationship with canopy levels than phenolics concentration. For example, carbohydrate reserves may be utilised for fruit maturation (to raise TSS levels) in those grapevines that have relatively low photosynthetic capacity to fruit weight ratios (see Candolfi-Vasconcelos et al 1994). On the strength of these results, confident forecasts of spatial variability in TSS across a vineyard could not be made based on canopy alone.…”

Effect of Postharvest Defoliation on Carbon and Nitrogen Resources of High-Yielding Sauvignon blanc Grapevines

“…fruit, are the priority sink for CHO during the last stages of ripening (Candolfi-Vasconcelos et al 1994a).…”

“…The capacity for reserve replenishment increases after midberry ripening (Candolfi-Vasconcelos et al 1994a). Loss of photosynthetically active leaf area or excessive crop loads may deplete storage reserves (Candolfi-Vasconcelos et al 1994b).…”