Phloem contents

Even the size of leaf disks may affect the outcome of preference tests, as smaller disks have relatively more wounded edge tissue that may affect the suitability of center tissue more than for larger disks (Jones Coleman 1988). Leaf disks are not recommended for work with sucking insects. Physiological changes seem to affect the phloem contents very rapidly (e.g., Muller 1966 van Emden Bashford 1976) and may well induce a generally unsuitable condition. 

When compared to whole meal rye flour (280 kcal/1160 kJ) and to wheat flour (320 kcal/1320 kJ), phloem powder (140 kcal/580 kJ) contains approximately 50% less energy. As is typical for all flours, phloem powder also contains a low amount of fat (total amount 2.3 g/100 g). The protein content of phloem is only 2.5 g (per 100 g), whereas the respective amount in whole meal rye flour is 8.8 g and in wheat flour 12.1 g. The content of carbohydrates in phloem ( 30 g/100 g) is about 50% less than in rye (55 g) and wheat flours (59 g). The relatively low energy, protein and carbohydrate content of phloem when compared with commonly used flours, is related to its high content of different fiber. Detailed nutritional data for phloem and phloem breads used in our trial are presented in Table 14.1. 

Table 14.1 The nutrient content of phloem powder and study breads per 100 g ...

Subjects were randomly assigned to consume daily 70 g of normal dried rye bread (placebo group, = 30), rye bread in which 8% of the rye flour was substituted with phloem powder (low phloem, LP, group, = 30) or bread in which 14% of the rye flour was substituted with phloem powder (high phloem, HP, group, n = 15). Study breads used in our study were different in fiber, lignan and catechin content. The nutrient content of the phloem powder and... 

Fromm and Spanswick [79] found that electrical stimulation of a plant is followed by ion shifts which are most striking in the phloem cells. While their content of potassium and chloride was diminished after stimulation, the amount of cytoplasmic calcium increased slightly (Table 1). These displacements lead to the conclusion that Ca + influx as well as and CP efflux are involved in the propagation of action potentials. The main difference between propagation of action potentials in animals and plants is that in an axon there is the K /Na transmembrane transport but in phloem cells the K /Ca channels are involved in this process [Fig. 22(b)]. 

The rate of maximum cation uptake has been shown to be dependent upon maximum levels of organic acids in the root cells (119,120). The organic acids, such as citric and malic acids, are transported from the sites of photosynthesis by the phloem while the cations are transported to the leaves by the xylem. Brown and Chaney (120) have suggested that iron uptake into the plant will be dependent upon the citric acid content of the root cells. 

The border between wood and bark is the cambium, which consists of only one layer of cells. This living cell layer produces xylem cells towards the inside of the stem and phloem cells towards the outside (Figure 1). In all the wood species studied, common characteristics of the cambium include a high content of pectins and the absence or low content of lignin (39, 40,... 

The content of pectins in the cambium cells varies between the wood species studied but may be as high as 40% of the dry weight. The content of pectic and hemicellulosic compounds is also high in the phloem 42),... 

The transport of toxic alkaloids in the phloem can be an advantage for plants against phloem-feeding insects, such as aphids [8], For example alkaloid-rich lupins are avoided by aphids, whereas sweet lupins with very low alkaloid contents are preferred by polyphagous aphids [8,22]. 

The correlation between nicotine accumulation and its defensive role in M sylvestris has been convincingly demonstrated. Increased alkaloid production may also be demonstrated by true herbivory. Tobacco plants subjected to leaf damage showed a fourfold increase in the alkaloid content of their undamaged leaves. This resulted from increased alkaloid synthesis and, as a result, a tenfold increase in alkaloids in the xylem. Experimental evidence has indicated that alkaloid induction maybe triggered by a phloem-translocated signal (Hartmann, 1991 and references therein). 

Warren-Wilson (285) has shown that the downward migration of the Atropa alkaloids is via the phloem, and experiments with lupines confirm this (271). Here the root content is determined lai ely by that of the aerial portion, as was shown by grafting bitter lupines on sweet lupines and on non-alkaloid bearing legume stock (271, 273). A similar migration to the seeds of a Pisum has been reported by others (272). 

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