RATNAYAKA, H. HARISH1*, WILLIAM T. MOLIN2, and TRACY M. STERLING1. 1Department of Entomology, Plant Pathology and Weed Science, New Mexico State University, Las Cruces, NM 88003; 2Southern Weed Science Research Unit, USDA-ARS, Stoneville, MS 38776. - Oxidative stress tolerance in cotton and spurred anoda under competition and drought.
Injury to plants due to environmental stress is mainly caused by the
reactive oxygen species that attack biomolecules and membranes. To
prevent this damage plants have evolved an antioxidative system
consisting of low molecular weight antioxidants such as ascorbate,
a-tocopherol, glutathione and carotenoids,
and of enzymes such as catalase, ascorbate peroxidase (APX) and
glutathione reductase (GR). Since competition among plants decreases
the availability of moisture and nutrients, it may initiate oxidative
stress in plants. We studied the effect of intraspecific and
interspecific competition on oxidative stress tolerance of cotton
under adequate supply of moisture and nutrients in greenhouse. Two
species of cotton (Gossypium hirsutum L., cultivar Delta Pine
5415, and Gossypium barbadense L., cultivar Pima S-7) were
grown alone or three plants per pot for intraspecific competition. One
plant of each of cotton species was grown with two plants of spurred
anoda [Anoda cristata (L.) Schlecht.], an important cotton weed
in the southern United States, for interspecific competition. A single
plant of spurred anoda was maintained per replication. These treatment
combinations were replicated six times. Net photosynthesis and
photosynthetic quantum yield were not influenced by planting design or
species at three weeks after planting. Chlorophyll a+b content was
greater in A. cristata and G. hirsutum than G.
barbadense. Carotenoid content was highest in A. cristata
and higher in G. barbadense than G. hirsutum. Two cotton
species had constitutively greater catalase and APX activities than
spurred anoda while G. hirsutum had greater GR activity. When
half of the experimental plants were subjected to a six-day drought,
APX activity increased by 62% in G. hirsutum and 66% in G.
barbadense; catalase and GR were unaffected. The levels of low
molecular weight antioxidants as influenced by competition and drought
will be presented.
Key words: Anoda cristata, competition, drought, Gossypium barbadense, Gossypium hirsutum, oxidative stress tolerance