Sulfur Burn in Citrus Radioactive Sulfur Used in Studies to Distinguish Between Fruit-Contained and Applied Sulfur

Sulfur Burn in Citrus radioactive sulfur used in studies to distinguish between fruit-contained and applied sulfur

F. M. Turrell and M. B. Chervenak

Radioactive sulfur tracers and a When kept in hydrogen sulfide gas at Sulfur is thought to be the important Geiger counter were used at the Riverside temperatures of 105" F to 120" F, citrus part of glutathione. Experiment Station in investigations fruits give off sulfur dioxide gas. When Not much is known about how sulfur made to learn how sulfur burns citrus fruits are kept in either hydrogen sulfide is used in a plant but it is thought that fruits-so sulfur could be safened. gas or sulfur dioxide gas, the sulfate con- radioactive sulfur must go into the pro- Sulfur dust and lime-sulfur sprays- tent of the peel and the acidity of the sap tein of the fruit peel before it can be because of their low cost-probably will in the peel are increased. Thus, when sup- made into radioactive sulfate. be used to a greater extent in pest control plied with hydrogen sulfide or sulfur A radioautograph of a peel section of a programs as citrus prices decline, even dioxide gas, citrus fruit peel of fresh in- radioactive sulfur-dusted lemon could be though sulfur burns the fruit during pe- tact fruit will produce sulfuric acid. obtained for the studies because radio- riods of hot weather. active sulfur acts like light on a photographic film. The substances in the peel Sulfur-resistant pests seldom develop- Radioactive Sulfur as houseflies resistant to DDT have devel- that dissolve in water and in alcohol were oped-which may be due to the fact that Radioactive sulfur tracers can be meas- taken out before the slice of peel was put sulfur affects sever'al enzyme systems. An ured in amounts much smaller than simi- on the photographic film. Only the cell enzyme is a substance in a living cell that lar substances that are not radioactive. walls and protein in the slice of peel were aids in the change of one substance to A few hundred thousand radioactive left. Since sulfur is not found in the cell another but which is not itself changed atoms-too small to see with a micro- wall, the radioactive sulfur must have in the process. scope-will make themselves known be- been in the protein. The multiple action-affecting several cause of the radio-like signal which each Sulfur dust changes slowly to a sulfur enzyme systems-of sulfur on pests is per- atom sends out. By using a Geiger coun- gas much more rapidly at high than at haps its chief drawback when used on ter, the signals the radioactive sulfur low temperatures. plants. atoms send out can be heard. The ordi- It is believed that sulfuric acid is the nary sulfur atoms in the plant do not end product of the chemical action of send out such signals. Small Amount citrus fruit peel on sulfur. High air tem- By dusting lemons with radioactive To show that a small amount of sulfur peratures along with the sulfuric acid are sulfur and keeping them at 105" F, it was gas will go into lemons, the following ex- thought to cause sulfur-burn. found that 100% of the hydrogen sulfide periment was tried : When oranges or lemons are dusted was radioactive; about 14% of the sulfur A dish of radioactive ground sulfur with ground sulfur and subjected to tem- dioxide gas was radioactive; and 77% of was placed at the bottom of a glass.bottle, peratures of 90" F to 140" F, hydrogen the sulfate in the peel was radioactive. and lemons piled above it in such a way sulfide-the rotten-egg gas-is given off Lemons kept at 105" .F give off water that they could not touch the sulfur. The by the fruit; a small amount of sulfur with sugars, pentosans, oil, iron, calcium, bottle was then heated to 106" F for sev- dioxide gas is produced; and the sulfate magnesium, sodium, potassium, am- eral hours. At the end of that time about content of the peel and the acidity of the monia, chlorides, phosphates, sulfates, 5.7% radioactive hydrogen sulfide, 1% peel sap are increased. These products in- and oxalates in it. The radioactive sulfate radioactive sulfur dioxide, and 2% radio- dicate that sulfuric acid is made from the in the water given off from lemons dusted active sulfate were obtained from anal- sulfur dusted on citrus fruits. with radioactive sulfur amounted to about Continued on page 14 83% of the sulfate in the water. The above experiments clearly show that sulfur dust somehow gets into the fruit peel; some of it is changed to hydrogen sulfide; and some of it is changed to sulfate. It appears that when there are not enough metals present in the peel sap to tie up the sulfate formed from the sulfur dust, the sulfate becomes sulfuric acid . The hydrogen for the hydro& sulfide may come from glutathione, a substance thought to be in all living cells which makes it possible for them to breathe.

Left. A photomicrograph of a radial section through the peel of a lemon dusted with radioactive sulfur and kept at 106°F.

Right. The image made an dental x-ray film- a radioautograph-made by the radioactive sulfur contained in the radial section shown in the illustration on the left. STORAGE In a single storage test of Valencia SULFUR Continued from page 7 oranges dipped in 2,4-D solutions, it was found that, as with the lemons, they de- Continued from page 4 to storage the grapefruit were washed veloped fewer black buttons than the non- yses of the lemon peel. Thus it was proved with 1/2"/0soap solution, then treated with treated fruit. ground sulfur can enter citrus fruits as 11/4%of Exchange Wax No. 22. sulfur vapor or gas. Compared to nonsprayed fruit, those Wm. S. Stewart is Associate Plant Physiolo- gist in the Experiment Station, Riverside. Sulfur vapor alone in a glass bottle sprayed with either eight or 16 pprn 2,4-D heated to the melting point of sulfur will had a reduced amount of surface decay, The above progress report is based upon Re- search Project No. 1346. combine with hydrogen to produce hy- aging and black buttons throughout the drogen sulfide. Oxygen is needed for this storage. There was also a decrease in in- The study initiated in January 1947 was a cooperative project between the Research De- reaction and sulfur dioxide is produced ternal Alternaria decay as shown by cut- partment of the California Fruit Growers Ex- in the process. ting the black button fruit after storage. change, Ontario, and the Division of Plant Glass tubes having the same surface as After 15 weeks of storage, the fruit Physiology of the University of California Citrus the lemons used in the experiments were Experiment Station, Riverside. from trees sprayed with 16 pprn 2,4-D sulfur dusted and placed in a bottle which was rated the best with regard to firm- was kept at 105" F. At the end of two ness, color and general appearance. The days time, no hydrogen sulfide nor sulfur eight ppm 2,4-D fruit rated next best, and POMEGRANATES dioxide gas had been formed. This, it is the nonsprayed fruit was the poorest of Continued from page 11 believed, shows that elemental sulfur the three lots. must get into citrus fruit to make hydro- being sharply delimited. The lower two gen sulfide and sulfur dioxide gases at 2,4-D Treatment After Harvest fruits have the blemish occasionally found atmospheric temperatures. On May 17, 1948, after washing and on pomegranates, but not associated with Plants need sulfur to build proteins. waxing, both light green and green lem- the mites. The checked and dark brown Sulfur, usually in the form of sulfate, is ons from non-2,4-D-sprayed trees were discolored areas coincide and are sharply supplied to plants through the soil. The dipped for two minutes in a lanolin emul- defined. There is no tendency for the sulfate may be put on the soil as a neutral sion containing either 500 or 1,000 pprn blemished area to be concentrated at the salt or as a weak solution of sulfuric acid. acid equivalent of the butyl ester of 2,4-D. stem end of the fruit. The roots absorb sulfate, but must be able Another sample of green lemons was to change the sulfate into other forms in exposed for 69 hours to the vapor of the Control order to build the sulfur into protein. isopropyl ester of 2,4-D. After exposure, In experiments made in 1948 it was the treated lemons were placed in the stor- Enzymic Action Suggested age chamber with the nontreated fruit. shown that all the commonly used mite treatments will control the Brevipalpus Inspection showed that after 115 days Another experiment was conducted to mit?, but since sulfur dust is highly ef- of storage at 58" F to 60" F and 88% observe what would happen if citrus fruit relative humidity, the nondipped light fective as well as being inexpensive, it is were dipped in weak radioactive sulfuric green lemons had 1.88% surface decay recommended as a control measure. Ex- acid and kept at about 115" F for several and 51.3% black buttons. perimental and commercial control treat- hours. The fruit yielded slightly radio- In contrast, after 162 days of storage, ments made in June and July 1948 with active sulfur dioxide and hydrogen sul- the light green 2,4-D-dipped lemons had one half pound of sulfur dust per tree, fide gases, very radioactive sulfate and only 376 with black buttons and none resulted in excellent control, while un- protein. The sap in the peel had become with Alternaria decay. At this time no treated check trees were severely infested, more acid. surface decay had developed on the with a high percentage of blemished fruit. It might be said in passing that the fruit dipped fruit compared to 3.85% on the Walter Ebeling is Associate Professor of En- resembled sulfur-burned fruit as did the nondipped. tomology and Associate Entomologist in the fruit kept at 105" F in hydrogen sulfide The green lemons dipped in either 500 Experiment Station, Los Angeles. or sulfur dioxide gas for a few hours. Roy J. Pence is Laboratory Technician in the This experiment suggests that enzymes or 1,000 pprn 2,4-D solutions had failed Division of Entomology, Los Angeles. to develop a single fruit with a black are present in the fruit peel which can The above progress report is based on Re- change sulfate to other forms of sulfur. button or Alternaria decay after 162 days search Project No. 1339. of storage. Surface decay was 0.60% for But the rate of change of sulfur to sulfate the dipped fruit compared to 12.25% for is a more rapid process than the one the nondipped. changing sulfate back to other forms of The 2,4-D vapor treatment of green ALMOND sulfur. lemons for 69 hours at the beginning of Continued from page 10 Experiments are under way to deter- storage also reduced black buttons and mine the effect of temperature on the rela- Alternaria decay as well as surface decay There is a great variation in the type tive rates of changing sulfur to sulfate or compared to nontreated fruit. The re- of hulls obtained in harvesting different vice versa. duction was much less than for the dip varieties of almonds. Certain hulls, such Other experiments in which lemons treatment. as the IXL which were used in this test, are being treated with radioactive hydro- are thick and meaty, while those from gen sulfide and sulfur dioxide are being some other varieties are thin and papery. run. This and other work probably will Wax Preparations The nutritive value of the hulls undoubt- bear out the evidence already found on In addition to the dip and vapor 2,4-D edly varies accordingly. It is planned to how ordinary elemental sulfur is changed treatments, 500 ppm 2,4-D as the butyl do further work on almond hull feeding to sulfuric acid. ester was added to the Exchange Water- this fall. Wax preparations. In comparison to non- ~ F. M. Turrell is Associate Plant Physiologist Robert F. Miller is Professor of Animal Hus- in the Citrus Experiment Station, Riverside. treated lemons in all color groups there bandry and Animal Husbandman in the Experi- M. B. Chervenak is Senior Laboratory Assist- was a remarkable reduction in percentage ment Station, Davis. ant, Citrus Experiment Station, Riverside. of fruit with black buttons, internal Alter- The above progress report is based on Re- The above progress report is based on Re- naria decay and surface decay. search Project No. 700. search Project No. 1200.

14 CALIFORNIA AGRICULTURE, JUNE, 1949