Source Sink Relations

 

PHLOEM AND XYLEM TRANSLOCATION

(Figure 3.9 and Table 3.8 from Marshner 1986, Summary from Bidwell 1974)

Fig 3 9  Long-distance transport in xylem (X) and phloem (P) in a stem with a connected leaf, and xylem-to-phloem transfer mediated by a transfer cell (T).

 

Table 3.8. Solutes in the Phloem and Xylem Exudates of tobacco.

⁴ND, Not detectable; NA, data not available., 'Milligrams per milliliter.

 

summary.  The general conclusions about the pathways and tissues of translocation:

1.                          Salts and inorganic substances move upward in the xylem.

2.                          Salts and inorganic substances move downward in the phloem.

3.                          Organic substances move up and down in the phloem.

4.                          Organic nitrogen may move up in the xylem (trees) or phloem (herbaceous plants).

5.                          Organic compounds like sugar may be present in the xylem sap in large concentrations during the spring when sap rises in trees before the leaves emerge.

6.                          Lateral translocation of solutes from one tissue to another occurs, presumably by normal mechanisms of transfer (osmosis, active transport, and so on).

7.                          Exceptions to these generalizations are known to occur.

CARBON MOBILIZATION

Redistribution Between Sources and Sinks

(Fig. 10.19 from Taiz and Zeiger 1998, Fig. 3.61 from Larcher 1980)

 

Figure 10.19   Autoradiographs of a leaf of summer squash (Cucurbita pepo), showing the transition of the leaf from sink to source status. In each case, the leaf imported ¹⁴C from the source leaf on the plant for 2 hours. Label is visible as black accumulations. (A) The entire leaf is a sink, importing sugar from the source leaf. (B-D) The base is still a sink. As the tip of the leaf loses the ability to unload and stops importing sugar, as shown by the loss of black accumulations in B through D, it gains the ability to load and to export sugar. (From Turgeon and Webb 1973, courtesy of R. Turgeon.)

 

 

Fig. 3.61. Variations in starch deposition by trees throughout the year. Maximal accumulation of starch is indicated by black, large amounts by cross-hatching, and small amounts by stippling; in the parts left white, starch is present in traces or not at all. Fagus sylvatica (Central Europe): 1, just before leaf emergence in the spring; 2, during leaf unfolding; 3, midsummer; 4, just before abscission in the autumn; 5, conversion of starch to soluble carbohydrates at low temperatures during winter. After Fischer (1891), Gaumann (1935), and K. Kober (unpubl.). Abies veitchii (Japan): 1, during growth of new shoots in spring; 2, late summer; 3, during winter frost. After Kimura (1969). Olea europaea (Northern Italy): 1, during shooting and flowering in spring; 2, during a dry period in midsummer; 3, in winter after the end of the rainy season. After Thomaser (1975). For the storage dynamics of Atlantic dwarf shrubs see Stewart and Bannister (1973), and Grace and Woolhouse (1973); of chaparral species, Mooney and Hays (1973); of mountain plants, Larcher (1977) and Zachhuber and Larcher (1978)

NUTRIENT MOBILITY

 

Redistribution Between Sources and Sinks

(Fig. 13-12 from Bidwell 1974, Table 3.9 from Marschner 1986)

 

Figure 13-12 (opposite). A sequence of six autoradiograms showing the fate of an aliquot of ³⁵S absorbed as ³⁵S0₄ during a 1-hr absorption period. The plants, after the hour in the nutrient solution containing the tracer, were removed to a normal (nonradioactive) solution where they remained for the following periods: A, 0 hr; B, 6 hr; C, 1 2 hr; D, 24 hr; E, 48 hr; and F, 96 hr. Most of the ³⁵S, which moved directly into the mature leaves, was withdrawn within 1 2-24 hr. It moved predomi­nantly into younger leaves near the stem apex, where it remained. [From 0. Biddulph: Plant Physio/. 33:295 (1958). Used with permission. Photograph courtesy Dr. Biddulph.]

 

Table 3.9. Mobility of Mineral Elements in Phloem

From Bukovac and Wittwer (1957).

DIAGNOSING NUTRIENT DEFICIENCIES

Based on Nutrient Mobility

(from Vetanovetz 1996)

 

Mobile Nutrients – deficiencies typically appear on older growth first.

 

Immobile nutrients – deficiencies typically appear on newer growth and shoot tips first

 

MONOCARPIC SENESCENCE

Changing Sources and Sinks During Vegetative and Reproductive Growth

(Fig. 1 from Egli and Leggert 1973, Fig. 3 from Harper 1971)

 

Fig. 1.   Dry matter accumulation patterns for Kent and D66-5566, 1971.

 

Fig. 3. Seasonal uptake and accumulation of N, P, K, Ca, and Mg by soybeans at weekly intervals¹ from field hydroponic gravel culture systems.

EPISODIC GROWTH OF TEMPERATE WOODY PLANTS

Cycling Between Shoot and Root Growth and Implications on Fertilizer Timing

(Fig. 2 on growth from Mertens and Wright 1978, Fig. 2 on uptake from Hershey and Paul 1983, Table 1 from Gilliam and Wright 1978)

 

Fig. 2. Root and shoot growth rates of 'Helleri' holly grown at 150 ppm N applied as 20N-8.7P-16.5K soluble fertilizer.

Fig. 2. Uptake rates for K+ and Mg2+ for a single plant of Euonymus japonica (plant 5). Bars indicate periods of shoot elongation

 

 

Table 1. Effect of the time and no. of weekly fertilizer applications during 1st growth flush on tissue N accumulation and sub­sequent shoot and root dry wt of 'Helleri' holly.