Carbohydrate Buildup in Girdled Wood

CARBOHYDRATE BUILDUP IN GIRDLED WOOD OF MACADAMIA TREES

Lois E. James, Marion Makaimoku and John L. Price

Reprint from CMS Yearbook 1970

In the procedure of grafting macadamias it has become common practice to use scions that have come from previously girdled branches. This practice has resulted in an increase in the number of successful grafts. It has been assumed that there is an accumulation of foodstuff above the girdle and that this gives the scion a better chance to take hold and grow.

That foodstuffs do accumulate above a girdle is well supported experimentally for many plants (Noel 1970). Most of the investigations have been concerned with changes in carbohydrates. Little information is available concerning the alterations in other kinds of foods, although Swanson (1959) has reviewed the changes in nitrogenous compounds resulting from girdling. Mittler (1958) measured the amino acid increase above the girdle in willow and Stoltz and Hess (1966) in Hibiscus. In general, auxins accumulate above a girdle since they are formed at the ends of branches and are transported downward (Jacobs 1961). However, Stoltz (1965) has reported a decrease in the auxin content in the girdled stem of Hibiscus.

There must be a proliferation of cambia cells for a successful graft. The exact role of accumulated foods and growth hormones on the vascular cambium in a girdled stem is not known.

The present experiment does not attempt to explain why girdling improves the chance for successful grafting in macadamias but only to determine the time after girdling of maximum carbohydrate buildup to determine if there is a correlation with the amount of carbohydrate and the degree of success in grafting.

Procedure — One branch from a M. integrifolia tree and another branch from a M. tetraphylla tree were girdled. The M. integrifolia was a vigorous seedling about 20 feet tall. The girdled branch was 17 inches from the base of the tree, 9 feet in length, and 11/2 inches in diameter where the girdle was made. The girdle was made 12 inches from the base of the branch. The M. tetraphylla tree was a hardy Santa Ana variety about 20 feet tall. The girdled branch was 13 inches from the base of the tree, 8 feet in length, 1 inch in diameter where the girdle was made. The girdle was 7 inches from ‘the base of the branch. In both branches the girdles were 1 /2 inches in length and in both cases branches were selected which were exposed to the south. Both branches had many laterals.

The branches were girdled November 5, 1969. Starting on November 6 and continuing first at intervals of every 2 days and later every 7-14 days, specimens from each branch were assayed for carbohydrate production. The specimens were branch laterals.

Pieces of stems, a few inches in length, are shaved as finely as possible. Approximately 4 grams per sample are used. The shavings are boiled immediately for about 15 minutes in 80% ethyl alcohol. About 1/4 gram of CaCo3 is added to the boiling shavings to prevent reactions of enzymes. The liquid, which now contains the soluble sugars leached from the plant tissue, is prepared for analysis of carbohydrate content. Through processes of evaporation and concentration, and finally, with the addition of Somogyi’s and Nelson’s reagent, the sample is prepared for photometric assay. The optical density of the sample is read from a Baush and Lomb Spectronic 20 colorimeter. A standard water and glucose series also is processed. The optical density is used to find the concentration of glucose by the formula:

Optical Density Known Concentration Known
=
Optial density Unknown Concentration Unknown

 

Solving for the unknown concentration gives the amount of glucose in the sample. Reducing sugars are determined by this procedure.

The second step involves the assay of the non-reducing sugars. These are more difficult to leach out of the plant tissue than are the reducing sugars. A subsample of 200 milligrams from the original 4 grams of tissue is refluxed with 80% ethyl alcohol in a Soxhlet extraction apparatus. This is recycled for 18-24 hours and then assayed in the same manner as reducing sugars.

The third step involves extracting and analyzing the amount of starch. The 200-milligram subsample from the step before is weighed, ground and left to digest to soluble sugars with the aid of Takadiastase. Progressively, it is then evaporated, condensed treated with Somogyi’s and Nelson’s reagent, and assayed by the colorimeter.

Thus, by extracting and processing the reducing sugars, non-reducing sugars and soluble starches, and then by utilizing their optical density to determine the glucose concentration of each, the total amount of carbohydrate reserve from the original 4 grams of plant tissue can be determined.

Results:

Milligrams of glucose per gram of tissue

Discussion — During the first 24 hours there was a decrease in carbohydrates in the girdled branches of both trees. This was followed by increases to the 30th day. Between the 30th day and 69th day the amount of glucose decreased. The amount of carbohydrate buildup in the M. integrifolia tree was considerably greater than in the M. tetraphylla tree. However, it can not be stated from these results that there will always be a consistent difference in the two species.

Baldwin (1939) states that there is not always an accumulation of sugar above a girdle. Noel (1965) has reported that if girdling is carried out after the spring flush, carbohydrates do not accumulate above the girdle because they have been utilized in the production of new leaf growth. The two trees used in our study did not flush until February, which was after the end of is experiment. If there is a correlation between carbohydrate storage and successful grafting, then there is need to test for carbohydrate buildup at the time of or shortly after flushing.

BIBLIOGRAPHY

Baldwin, H.I. 1934. Some physiological effects of girdling northern hardwoods. Bull. Torrey Bot. Club 61:249-257.

Jacobs, William P. 1961. The polar movement of auxin in the shoots of higher plants: Its occurrence and physiological significance. Fourth International Conference of Plant Growth Regulation pp. 397-409

Muffler, T. E. 1958. Studies on the feeding and nutrition of TUBEROLACHNUS SALIGNUS (Gmelin) (homoptera, Aphididae). II. The nitrogen and sugar composition of ingested phloem sap and excreted honeydew. Jour. Exp. Biol. 35:74-84.

Noel, A.R.A. 1965. The effects of girdling upon some trees in Central Africa. Ph.D. Thesis, University of London.

Noel, A.R.A. 1970. The girdled tree. Botanical Review 36:162-195.

Stoltz, L.P. 1965. Physiological study of the effect of girdling upon rooting. Diss. Abstr. 26:1739-1740.

Stoltz, L.P. & C.E. Hess. 1966. The effect of girdling upon root initiation:

Carbohydrates and amino acids. Proc. Amer. Soc. Hort. Sci. 89:734-743. Swanson, C.A. 1959. Translocation of organic solutes. In: F.C. Steward "Plant Physiology’ 2:481-511.