P. Brouwer

Bio: P. Brouwer is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 63 citations.

Sink strength as a determinant of dry matter partitioning in the whole plant

Abstract: Dry matter partitioning is the end result of the flow of assimilates from source organs via a transport path to the sink organs. The dry matter partitioning among the sinks of a plant is primarily regulated by the sinks themselves. The effect of source strength on dry matter partitioning is often not a direct one, but indirect via the formation of sink organs. Although the translocation rate of assimilates may depend on the transport path, the transport path is only of minor importance for the regulation of dry matter partitioning at the whole plant level. To understand the regulation of dry matter partitioning by the sinks, a parameter like sink strength is needed that describes a sink's ability to influence assimilate import and is independent of the rest of the plant. The term sink strength can be defined as the competitive ability of an organ to attract assimilates. However, there is much debate and confusion about the term sink strength because this term is often not clearly defined. Sink strength has been proposed to be the product of sink size and sink activity. Although cell number is often considered as a suitable measure of sink size, it appears not always to be an important determinant of sink size. Moreover, sink strength may depend on sink age rather than sink size. A model for dry matter partitioning into generative plant parts, which is based on sink strengths of the organs, is described. The potential growth rate (potential capacity to accumulate assimilates) has been shown to be an important parameter that quantitatively reflects the sink strength of an organ. The potential growth rates of the plant's organs are not static but change dynamically. The potential growth rate of a fruit is a function of both its age and temperature. For several crops it has been shown that the dry matter partitioning into an organ can be quantitatively described as a function of its potential growth rate relative to that of the other plant organs.

Influence of Light on Grape Berry Growth and Composition Varies during Fruit Development

Abstract: Potted 'Cabernet Sauvignon' and 'Pinot noir' grapevines ( Vitis vinifera L.) grown in a sunlit phytotron were used to study the influence of cluster light exposure during various stages of fruit development on berry growth and composition. Clusters grown without light during berry development stages I and II, stage III, or stages I, II, and III, were compared to clusters exposed to light throughout fruit development (control). The temperature of light-exposed and nonexposed fruit was similar. The weights and diameters of berries grown without light during stages I and II, or stages I, II, and III, were similar and significantly lower than those of the control. Fruit softening in both cultivars, as well as the initiation of berry coloration, was delayed when berries were grown without light during stages I and II. Following fruit softening, berries grown without light during stages I, II, and III were lower in sugar than the control. On the final sample date, 'Cabernet Sauvignon' berries grown without light during stages I, II, and III were higher in malate compared to the control. 'Pinot noir' berries grown without light during stages I and II, or stages I, II, and III, were lower in malate before fruit softening, and higher in malate following fruit softening, than the control. Control berries had greater skin anthocyanins and phenolics compared to the remaining treatments. Berries grown without light during stages I and II, or stage III, were greater in anthocyanins and phenolics than fruit grown without light during stages I, II, and III. Light had no effect on fruit tartrate concentration or juice pH. Light had its greatest impact on fruit development during the initial stages of berry growth. Berry growth was reduced and ripening delayed when fruit were grown without light during stages I and II. Normal fruit development was not fully restored when these fruit were exposed to light during stage III.

Flower and fruit abortion in sweet pepper in relation to source and sink strength

Abstract: Source strength (assimilate supply) and sink strength (assimilate demand) of the plant were varied in different ways to investigate to what extent flower/fruit abortion in sweet pepper (Capsicum annuum L.) is determined by the availability of assimilates. Source strength was varied by changing the light level, plant density, and leaf pruning. Sink strength was varied by changing the temperature and the number and position of earlier formed fruits. Shading as well as heating for short periods showed that flowers/fruits were the most susceptible to abortion during the first week after anthesis. The different experiments where source strength was varied all showed that when source strength decreased, the rate of abortion increased linearly, whether source strength was decreased by shading, high plant density, or leaf pruning. That flower and fruit abortion not only depends on the source strength but also on the sink strength of competing organs is shown by varying the number or the position of earlier formed fruits. With the same source strength, the rate of abortion showed a close relationship with the growth rate of the earlier formed competing fruits, suggesting that the induction of abortion by earlier formed fruits is due to their sink strength. Most of the variation in abortion could be related to differences in vegetative growth rate, the latter being an indicator of the source-sink ratio. However, with the same vegetative growth rate, the rate of abortion was lower for the leaf pruning treatments where no competing fruits were retained than for the fruit load treatments. This indicates that although most of the variation in abortion can be related to the source and sink strength of the plant, some effects of competing fruits can only be explained by a combination of competition and dominance.