Light-dependent Elongation of Anaerobically Maintained Green Pea Stem Segments and Its Implications

Abstract

Anaerobic conditions reversibly inhibit the elongstion of isolated green pea (Pisum sativum L. var Alaska) stem segments. Mlununation of segments maintaned under anoxia causes a resumption of growth. Po-laographic studies show pea stem segments are pbotosyntheticaly competent as determined by 02 evolution. Although 02 production is totaly inhibited by dichlorophenyldimethyluren (DCMU) and dinitrophenol (DNP) inhibits 02-dependent growth, neither DCMU nor DNP completely abolishes light-dependent growth, although both reduce the effect markedy. Phenazine methosulfate promotes the growth of anaero-bicaly maintained, Numinated, DCMU-treated segments. The data indicate that the princpal effect of light in inducing growth under anaerobic conditions is the photosynthetic provision of 02 for respiration. There is also some evidence that, at least in the absence of 02, a small amount of elongation is due to some other light-driven process, perhaps cyclic photophosphorylation. We have shown previously (12) that anaerobiosis reversibly inhibits the elongation of green pea stem segments. Under an-oxia, growth decreases rather abruptly to a low rate and thereafter decays slowly to zero. Shrinkage of the segments usually becomes evident after 3 to 4 hr. We have found, however, that this inhibition of growth and the subsequent shrinkage can be completely abolished by illumination of the segments. The light-dependent growth under O2-deprived conditions has been investigated to determine its mechanism and the possible implications on growth under more "nattral" conditions. Light-dependent growth under anoxia might be due to: (a) photosynthetic 02 evolution with restoration of aerobic conditions and respiration; and/or (b) contribution of some other growth-limiting intermediate by the chloroplasts. We shall show that at least the first proposal obtains, and provide indirect evidence for the second. MATERIALS AND METHODS Peas (Pisum sativum L. var Alaska) were grown in moist vermiculite in a glasshouse. One-cm segments were excised from the expanding second or third internode of 9-to 11-day-old plants. Segments were placed in 20 mm K-phosphate buffer (pH 6.2) and vacuum-infiltrated. If not used immediately, the stem segments were held at 3 C with vigorous aeration. Growth measurements were performed as previously described (12) with only slight modifications of the growth measur-' Current address: Department of Agronomy, University of Ne-braska, Lincoln, Neb. 68583. ing device (Fig. 1). All experiments were performed at 20 C within the water-jacketed growth chamber. Removal of 02 from the buffer for anaerobic treatments was difficult. Although the buffer was deoxygenated in the reservoir from which it was pumped, 02 was re-entering the system (primarily through the tubing of the peristaltic-type pump). The pump head was therefore enclosed with parafilm and flooded with N2. This reduced 02 levels in the growth chamber to less than 10 AM, a concentration which rapidly inhibited growth. In some experiments, buffer was not pumped past...

Photosystem II and Hypoxic Quiescence in Alligatorweed

“…In conclusion, our data agreed with previous data of Quimby and Kay (1977) and Parrish and Davies (1976). Oxygen produced by photosynthesis was apparently involved in some respiratory activity that prevented or relieved hypoxic quiescence.…”

“…Inhibitor, type and name under submerged (hypoxic) conditions. The relief by hydrogen peroxide of the simazine-induced inhibition of growth (Table 3) is somewhat analogous to the oxygen-stimulated growth of DCMU-treated green pea stem segments as reported by Parrish and Davies (1976). Quimby and Kay (1977) previously reported that hydrogen peroxide relieved the inhibition of growth of alligatorweed submerged in the dark and that oxygen relieved the inhibition of growth in a nitrogen atmosphere.…”

“…Quimby and Kay (1977) previously reported that hydrogen peroxide relieved the inhibition of growth of alligatorweed submerged in the dark and that oxygen relieved the inhibition of growth in a nitrogen atmosphere. Parrish and Davies (1976) recorded the responses of green pea stem segments over periods of 6 h or less, whereas we recorded the responses of alligatorweed after periods of 1 week to 12 days. Because of the longer exposure to the experimental conditions, the alligatorweed system had more potential for reflection of sprouting and subsequent growth under natural conditions.…”

“…Hypoxic quiescence is relieved by addition of oxygen to a nitrogen atmosphere when stem cuttings of alligatorweed are emersed in the dark, or by periodic ' addition of hydrogen peroxide when submerged in the dark (Quimby and Kay 1977). Parrish and Davies (1976) have reported that elongation of green pea (Pisum sativum L. cv. Alaska) stem segments was similarly inhibited by low oxygen, but this inhibition was relieved by illumination.…”

“…Alaska) stem segments was similarly inhibited by low oxygen, but this inhibition was relieved by illumination. Parrish and Davies (1976) concluded that the principal effect of light in inducing growth under anaerobic conditions is the photosynthetic production of oxygen for respiration. The alligatorweed system reported herein and in a previous paper (Quimby and Kay 1977) involved both sprouting and elongation, whereas the green pea stem system involved elongation only.…”