OBITUARIES

Arthur Galston. PHOTO COURTESY OF MICHAEL MARSLAND.

Remembering Arthur W. Galston
April 21, 1920–June 15, 2008

During his career, Arthur Galston’s research focused on how light, hormones, and polyamines regulate the growth and development of plants. From the time he returned to Yale as a professor of botany in 1955, his lab attracted an international group of graduate students, postdoctoral fellows, and visiting faculty from Europe, Israel, the Middle East, Africa, Central America, Asia, and Australia. Many returned home to become leading scientists in their own country.

This account touches only a few highlights among the great number and variety of his research projects. The interaction of phytochrome, flavonoids, and peroxidase activity was an early focus. Art’s graduate student Masaki Furuya, working with Art and Bruce Stowe, isolated two new flavonoids from peas. One, a conjugate of quercetin, inhibits activity of peroxidase, an enzyme capable of oxidizing IAA; the other, a kaempferol conjugate, is a peroxidase cofactor. These two flavonoids differ by an additional hydroxylation on quercetin, which they showed to be under control of phytochrome.

Brief red light increased the content of the peroxidase inhibitor and growth of terminal buds of peas but increased the cofactor and decreased growth of the youngest internode below. Over the years, the question of whether light-modulated patterns of growth involve flavonoids, perhaps by affecting peroxidase activity and auxin concentration, motivated much work in Art’s group, to which Bill Hillman, Harry Smith, W. Bottomley, D. Russell, and others contributed.

With Mark Jaffe, Art initiated an extensive series of physiological experiments on coiling of tendrils of peas. This led to the first report of a contractile ATPase with the characteristics of actomyosin associated with rapid movements in a higher plant. They also detected unusually high levels of conjugates of quercetin in uncoiled tendrils, which fell during coiling. They suggested that the decline of this flavonoid might activate ATPase and energize coiling.

Art collaborated with Ruth Satter and others investigating the interaction between phytochrome and circadian rhythms in the characteristic sleep movements of leaves of certain legumes. They observed that as the leaves open or close, motor cells contract on one side of the pulvinus and expand on the other. They showed that expansion and contraction of the motor cells reflect changes in turgor caused by rapid fluxes of both potassium and chloride ions. Further, they demonstrated an effect of phytochrome on these ionic movements. Open leaflets preirradiated with red light lost K+ from contracting motor cells and closed in the dark, whereas open leaflets preirradiated with far-red gained K+ and remained open.

Art enjoyed a scientific collaboration with Ravindar Kaur-Sawhney for more than 40 years. In the late 1970s, they found that culturing oat leaf protoplasts in the presence of arginine slowed senescence. Further, these protoplasts accumulated a high titer of putrescine, opening a major new research area on polyamines, abundant in plant cells. Art’s lab accounted for their synthesis and titer during growth, osmotic and other stress, development of flowers and fruit, and senescence. Graduate students Hector Flores and Nevin Young showed that stress-induced synthesis of putrescine results from increased activity of the arginine, rather than ornithine, decarboxylase pathway.

As discussed above, in etiolated pea seedlings red light increases growth in the apical bud but decreases it in the internode below. This effect correlates with synthesis of arginine decarboxylase and consequent increase in polyamines. The final research paper from Art’s lab showed that flowers of Arabidopsis have higher titers of both spermidine and putrescine than other parts of the plant. Furthermore, inhibiting polyamine biosynthesis inhibited flowering. Supplying spermidine in the medium overrode photoperiodic control, promoting flowering under short-day conditions where there would otherwise be little flowering. Art hoped his work on polyamines made obvious their importance in plants.

Early in his career, while a senior research fellow at Caltech, Art observed that in the presence of riboflavin, auxin was destroyed by light, and he provocatively suggested that a flavoprotein might be the long-sought blue-light receptor in phototropism. He also pointed out that the action spectra for phototropism—that had been thought indicative of a carotenoid photopigment—bore a resemblance to his action spectrum for the photo-oxidation of auxin by an extract from peas containing both flavoprotein and peroxidase. During the 1950s, these results reawakened interest in both the means of auxin redistribution during phototropism and the nature of the photoreceptor. Winslow Briggs extended and corroborated F. W. Went’s earlier work showing that during phototropic curvature, auxin is not destroyed and curvature is blocked by barriers to lateral movement of auxin. Almost simultaneously, George Curry produced a definitive action spectrum for phototropism of oat coleoptiles showing significant fine structure in the blue characteristic of carotenoid pigments, but a broad band in the near ultraviolet, suggestive of a flavoprotein.

Clearly, the photoreceptor question could not be settled without further evidence. Art searched for mutants. The few corn and barley mutants deficient in carotenoids proved nearly as phototropically sensitive as normally pigmented plants, even with as little as 0.1% of the normal amount of carotenoids, strengthening his skepticism about carotenoids being the photoreceptor. No flavin mutants were available, this condition apparently being lethal. Art turned to more accessible problems, and although he recognized that auxin destruction was not involved in phototropic curvature, he continued to maintain that the photoreceptor might be a flavoprotein.

It was 50 years before new technologies and Arabidopsis mutants with reduced phototropic responses provided the answer in the Briggs laboratory. The photoreceptor is a flavoprotein—named phototropin—whose fluorescence excitation spectrum bears an impressive resemblance to Curry’s action spectrum for phototropism. In the end, Art Galston was pleased that his suggestion that a flavoprotein could be the photoreceptor proved correct.

Mary Helen M. Goldsmith
Professor Emerita
Department of Molecular, Cellular, and Developmental Biology
Yale University