A DEVELOPMENTAL STUDY OF THE LEAVES OF NICOTIANA GLUTINOSA AS RELATED TO THEIR SMOG–SENSITIVITY

GLATER, RUTH BOBROV, RICHARD A. SOLBERG, and FLORA M. SCOTT. (U. California Los Angeles, and Los Angeles County Air Pollution Control District.) A developmental study of the leaves of Nicotiana glutinosa as related to their smog-sensitivity. Amer. Jour. Bot. 49(9): 954970. Illus. 1962.-Plants growing in the fields of Los Angeles County as well as those experimentally fumigated in the laboratory show gross markings in response to smog which vary from species to species, from a glistening appearance of the leaf undersurface due to a temporary accumulation of water in the affected cells through complete necrosis. In dicotyledonous leaves, "silvering," "bronzing," brown-black mottling or an increase in anthocyanin may be seen. In monocotyledons, transverse banding, tan in color, or longitudinal streaking of leaves are the usual responses. This damage appears in a characteristic pattern on the leaves, different from that produced by other phytotoxicants. Nicotiana glutinosa plants were grown in the air-filtered greenhouses at UCLA. The normal anatomical development of the foliage was studied and correlated with its susceptibility to smog injury. On a given plant, leaves of different ages show damage in different positions. Very young leaves at the apex of the plant and old leaves at the base of the plant are not sensitive. Expanding leaves between young and old in age are sensitive; in this group a distinct pattern of damage is discernible. Damage markings in the youngest leaves appear only at the tip; in leaves somewhat older, close to midblade; in fully mature leaves, only at the base. This localization of damage is shown to be correlated with the gradient of cellular differentiation from tip toward base as the leaf matures. Those cells which have just attained maximum size (young mature) are sensitive; damage, therefore, is a function of cellular development and maturity. The following anatomical details were analyzed: (1) differentiation and distribution of stomata and their opening and closing on both upper and lower epidermal surfaces and (2) development of intercellular air spaces in palisade and spongy parenchyma tissue. These studies indicate that damage occurs in the region of the leaf where stomata have just become functional and ambient polluted air can make direct contact with interior leaf tissues by virtue of large substomatal chambers and intercellular air spaces. THE GROSS appearance of crop damage is a standard tool today in determining the presence of a given atmospheric pollutant. Crocker (1948) discussed the pioneer experimental work done at Boyce Thompson Institute on plant responses to various gases. Thomas (1961) has presented an excellent compendium of all of the work through the years on this subject, including the recent work on the effects of the Los Angeles-type smog on vegetation. Gross symptoms of smog damage in the field vary with each crop, from a glistening appearance of the leaf undersurface due to a temporary accumulation of water in the affected cells, to complete necrosis (Bobrov, 1956). In dicotyledons, smog damage may be recognized as "'silvering" in spinach, "bronzing" in Romaine lettuce, brown-black mottling in tomato, or an increase in anthocyanin in table beet. In mono1 Received for publication March 19, 1962. 2 Present address: Department of Engineering, University of California, L.A. 24, Calif. 3 Present address: Department of Botany, Montana State University, Missoula, Montana. This study was aided in part by funds from the United States Public Health Service, Grant S17C. cotyledons, transverse banding, tan in color, is the characteristic response in barley and Poa (Bobrov, 1955b), while longitudinal streaking is characteristic of oat (Bobrov, 1952), corn, and many grasses. The chemistry of the highly oxidizing Los Angeles smog has been extensively treated in the literature during the past decade. The early work of Haagen-Smit et al. (1952) made it apparent that crop damage as it occurred "naturally" in the field could be reproduced in the laboratory by treating "pure"4 plants with the reaction products of ozone and many olefins (unsaturated hydrocarbons). The presently accepted reaction scheme for smog formation, as given by Scott et al. (1957), Stephens et al. (1961) and Schuck and Doyle (1959), indicates that olefins and nitrogen oxides react in the presence of sunlight. The ultraviolet radiation present in sunlight causes photolytic dissociation of NO2 to NO and atomic 4 "Pure" plants are germinated and grown in carbonfiltered greenhouses. Not a single trace of smog has been introduced during their life in the greenhouse prior to exposure to contaminated atmosphere.