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

Abstract

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): 954–970. 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.