Buxton Katrina N, Clearwater Michael J, Giles-Hansen K, Hewett E W, Ferguson Ian B
Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland, New Zealand.
The Horticulture and Food Research Institute of New Zealand, Te Puke Research Centre, RD 2, Te Puke, New Zealand.
Funct Plant Biol. 2007 Dec;34(11):1029-1037. doi: 10.1071/FP07091.
Excreta of the meadow spittlebug [Philaenus spumarius L. (Homoptera: Cercopidae)] feeding on leaves and pedicels of kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa 'Hayward'] were collected from insects from two different positions in the vine: from long, non-terminating axillary shoots producing fruit that are high in Ca and low in K and from short-terminating axillary shoots producing fruit that are low in Ca and high in K. The Ca, Mg, K and P concentrations in the excreta were determined, and found to be similar to those in the xylem sap. Daily and seasonal changes in xylem sap composition were compared in excreta collected from the two different shoot types. On average, Ca and Mg concentrations were higher and K and P concentrations were lower in xylem sap collected from pedicels on long, non-terminating axillary shoots than in sap collected from pedicels on short-terminating shoots. Differences in the mineral concentration between these two shoot types may therefore be due to differences in the xylem sap mineral concentration reaching the fruit. There was no measurable gradient in xylem sap composition within the parent shoots that could explain the differences between sap composition of the two axillary shoot types. Long, non-terminating shoots had higher leaf area, were more exposed, had higher stomatal conductance and rates of transpiration, and more negative leaf water potentials than short-terminating shoots. The higher xylem sap Ca and Mg concentrations of long shoots were therefore associated with higher rates of water transport to the long shoots. Xylem sap concentration differences between these two shoots types may have been because of differential loading or unloading of minerals between shoot types, associated with differences in transpiration rate or shoot growth rates. The higher transpiration rate of long shoots may cause phloem immobile minerals such as Ca to accumulate to higher levels at cation exchange sites in the shoot apoplast, resulting in increased xylem sap concentrations arriving at the fruit.
从猕猴桃[美味猕猴桃（A. Chev.）C.F. Liang和A.R. Ferguson var. deliciosa 'Hayward']叶片和果梗上取食的草地沫蝉[Philaenus spumarius L.（同翅目：沫蝉科）]的排泄物，是从葡萄藤上两个不同位置的昆虫收集而来：一个来自长的、不封顶的腋生枝条，这些枝条上结的果实钙含量高而钾含量低；另一个来自短的、封顶的腋生枝条，这些枝条上结的果实钙含量低而钾含量高。测定了排泄物中钙、镁、钾和磷的浓度，发现与木质部汁液中的浓度相似。比较了从两种不同枝条类型收集的排泄物中木质部汁液成分的每日和季节性变化。平均而言，从长的、不封顶的腋生枝条的果梗收集的木质部汁液中钙和镁的浓度高于从短的、封顶的枝条的果梗收集的汁液，而钾和磷的浓度则较低。因此，这两种枝条类型之间矿物质浓度的差异可能是由于到达果实的木质部汁液矿物质浓度不同。在母枝条内木质部汁液成分没有可测量的梯度，无法解释两种腋生枝条类型汁液成分的差异。长的、不封顶的枝条叶面积更大，更易暴露，气孔导度和蒸腾速率更高，叶片水势比短的、封顶的枝条更负。因此，长枝条较高的木质部汁液钙和镁浓度与向长枝条更高的水分运输速率相关。这两种枝条类型之间木质部汁液浓度的差异可能是由于枝条类型之间矿物质的不同装载或卸载，与蒸腾速率或枝条生长速率的差异有关。长枝条较高的蒸腾速率可能导致韧皮部不移动的矿物质如钙在枝条质外体的阳离子交换位点积累到更高水平，从而导致到达果实的木质部汁液浓度增加。
