The results of the greenhouse tests are shown in Table II and expressed as a percent of yield or uptake of nutrients from the standard sources. The response to nitrogen or phosphorus of the standard fertilizers was two to five times that of the no-nitrogen or no-phosphorus controls, thereby assuring valid comparison among the different nutrient sources. RESULTS AND DISCUSSIONThese experiments clearly show that long-chain crystalline ammonium and potassium ammonium polyphosphates are effective sources of N and P. As shown in Table II, all of the long-chain polyphosphates were good sources of N, although N uptake tended to be slightly lower than from ammonium nitrate. The long-chain polyphosphates prepared from furnace acid gave responses equivalent to or higher than that of monoammonium orthophosphate, but those products made from wet-process acid were slightly less effective.Most of the long-chain polyphosphates were low in available P (citrate + water soluble) and one sample contained only 27 % of its total P in an available form, as shown in Table II. Thus, the conventional availability test indicates that these polyphosphates could not be useful sources of P for growing plants. In spite of their low rating in the availability test all were effective fertilizers, and the results from fine and granular sources showed the usual granule size response obtained from water-soluble P sources in Mountview soil. Apparently, the rate of dis-solution in the soil was sufficient to give agronomic response typical of water-soluble sources. Therefore, the conventional availability test is not valid for these longchain polyphosphates.This investigation has shown that long-chain crystalline ammonium or potassium ammonium polyphosphates may be readily produced by thermal dehydration of orthophosphates or short-chain polyphosphates, and these highly condensed phosphates are effective sources of N and P.

Glutathione conjugation (GS-atrazine) of the herbicide, 2 -chloro -4 -ethylami no -6 -isopropylamino-s-triazine (atrazine) is another major detoxication mechanism in leaf tissue of corn (Zea mays, L.). The identification of GS-atrazine is the first example of glutathione conjugation as a biotransformation mechanism of a pesticide in plants. Recovery of atrazine-inhibited photosynthesis was accompanied by a rapid conversion of atrazine to GS-atrazine when the herbicide was introduced directly into leaf tissue. N-Dealkylation pathway is relatively inactive in both roots and shoots. The nonenzymatic detoxication of atrazine to hydroxyatrazine is negligible in leaf tissue. The hydroxylation pathway contributed significantly to the total detoxication of atrazine only when the herbicide was introduced into the plant through the roots. The metabolism of atrazine to GS-atrazine may be the primary factor in the resistance of corn to atrazine.The selective herbicides 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-striazine (simazine) are used extensively to control annual weeds in fields of corn and sorghum. These compounds are effective inhibitors of the Hill reaction in photosynthesis (7) and also reduce the rate of "4CO2 fixation in plants (1, 16).The rate of atrazine metabolism in higher plants is an important factor in herbicidal selectivity (9). Detoxication of atrazine was reported to occur by the 2-hydroxylation and N-dealkylation pathways in higher plants (9, 10). In sorghum a rapid conversion of atrazine to a water-soluble compound (metabolite B) resulted in a recovery of atrazine-inhibited photosynthesis (14). The subsequent identification of metabolite B as a mixture of two closely related compounds, GS-atrazinel and y-glutamyl-S-(4-ethylamino-6-isopropylamino-2-s-triazino)cysteine, indicated the presence of a third detoxication pathway present in higher plants (6). In this paper, the mixture will be referred to as GS-'

The primary factor for atrazine selectivity in corn (Zea mays) is the activity of a soluble enzyme, glutathione Stransferase, which detoxifies atrazine by catalyzing the formation of an atrazine-glutathione conjugate (GSatrazine). The nonenzymatic, benzoxazinone-catalyzed hydrolysis of atrazine to hydroxyatrazine contributed to the total resistance of corn to atrazine, but the nonenzymatic detoxication pathway does not seem to be essential for resistance. All corn lines investigated, except for susceptible GT112, rapidly detoxified atrazine by glutathione conjugation. Only GT112 had low glutathione S-transferase activity. Hydroxyatrazine was found in significant quantities only when atrazine was introduced initially into the roots. The amount of hydroxyatrazine formed was nearly equal for susceptible GT112 and most of the resistant corn lines investigated. This investigation indicates that some plants protect themselves against toxic organic hialide compounds witlh a mechanism similar to that known to exist in animals. and the closely related metabolite 'y-glutamyl-S-(4-ethylamino-6-isopropylamino-2-s-triazino)cysteine from resistant sorghum indicated the presence of a third metabolic pathway for atrazine degradation (15). N-Dealkylation was previously identified as another atrazine degradation pathway in plants (23,24). The recovery of atrazine-inhibited photosynthesis in both sorghum and corn leaf discs was accompanied by a rapid conversion of atrazine to GS-atrazine rather than to hydroxyatrazine (24, 25). The two peptide-conjugated metabolites will be referred to collectively in this paper as GS-atrazine since both compounds chromatograph as a single spot (metabolite B) (24) upon separation by thin layer chromatography (15).The isolation and characterization of the enzyme, glutathione S-transferase, from corn, sorghum, and other resistant species, indicated an enzymatic reaction for the formation of GS-atrazine (6). The presence of this highly active enzymatic pathway in corn leaf tissue suggests that the formation of GS-atrazine is the key factor in the resistance of corn to atrazine (25). This investigation was undertaken to show that the principal factor for atrazine selectivity in corn was the enzymatic formation of GS-atrazine rather than the nonenzymatic hydrolysis of atrazine to hydroxyatrazine as reported (3,7,11,18). MIATERIALS AND METHODSThe substituted s-chlorotriazines, atrazinel and simazine, are two of the most widely used herbicides for the control of annual weeds in fields of corn and sorghum. Both of these herbicides are believed to be metabolized similarly in plants, and their mode of action is the same. These compounds are effective inhibitors of the Hill reaction in photosynthesis (5, 16) and are known to reduce the rate of CO2 fixation in plants (1,27,29).Resistance of corn to the 2-chloro-s-triazines has been attributed to the nonenzymatic detoxication of the herbicides to hydroxyatrazine and hydroxysimazine (3,7,11,18). The nonenzymatic hydroxylation reaction was catalyzed by a...