The Effectiveness of the Spectrum in Chlorophyll Formation

Abstract

PROBLEMLight is essential for chlorophyll formation in higher plants, and it is likely that this process involves the building up of a light-sensitive precursor in the dark, and the subsequent formation of chlorophyll upon radiation. That such a precursor exists has been demonstrated many times since Pringsheim first recognized it in 1874. He observed an absorption band at 620 to 640 mg in an extract of etiolated leaves, corresponding to a substance which he named etiolin. Monteverde, in 1893, obtained essentially the same result from a spectroscopic examination of extracts of wheat, maize, and sunflower. He called this red-absorbing pigment protochlorophyU, the name by which it is most commonly known today. Lubimenko ~1928) believed protochlorophyll to be a breakdown product of the true chlorophyll precursor, chlorophyllogen, because he was unable to identify protochlorophyll in living plants. Subsequently the protochlorophyll band was observed in living, etiolated leaves of Zea plants (Scharfnagel, 1931), establishing it as a natural component of etiolated plants. However, it is not possible to observe directly the conversion of protochlorophyll into chlorophyll in the living plant (Noack and Kiessling, 1929) because the appearance of the strong absorption band of chlorophyll at 620 to 640 m/~ would mask the protochlorophyll band in the same place.Protochlorophyll has not been isolated in pure state, but chemical studies have been conducted on impure extracts of the inner seed coats of the pumpkin seed, which contain a greenish substance with the protochlorophyU absorption bands (Noack andKiessling, 1929, 1930). This work reveals the presence of a magnesium-rich molecule with porphyrin-like 15roperties. It remained for Fischer, Mittenzwei, and Oestreicher (1939) working on the same experimental material, to identify the molecule as the phyUin of vinylpheoporphyrin ai phytyl ester, in other words differing from chlorophyll a only in lacking two hydrogens in the 7, 8 position.Nevertheless, the main question conceming the pumpkin seed protochlorophyll still remains unanswered: is this substance the true precursor of chlorophyU, or is it a breakdown product of chlorophyll? Both lines of thought can be found in the literature.The basic fact remains that in etiolated plants there is a substance which

Effect of Light Quality, Light Intensity and Temperature on Pigment Accumulation in Barley Seedlings

“…while others report the blue to be most effective (1,5). The same disparity exists for carotenoid accumulation (14,18,19).…”

Control of Chlorophyll Production in Rapidly Greening Bean Leaves

“…Depending upon environmental conditions and plant material, it may continute for as long as 24 to 48 houirs (36). The action spectrum for chlorophyll production dturing this stage has not been determined, but it is very likely that 1 comaponent corresponds to the abhorpti'on spectrum of protochklorophyllide a (9,38).…”

Comment on “Catalytic Efficiency of a Photoenzyme—An Adaptation to Natural Light Conditions” by J. Popp et al.

“…Schmidt [6] made an attempt with maize seedlings a century ago, which can be regarded as semi-quantitative only. [7] This conclusion was later shown to be erroneous. [7] Because the equipment available at the time necessitated exposure times of several hours, secondary processes interfered with the primary conversion process, and the internal shielding of blue light by carotenoids was not thought to be important.…”

“…In 1946, Frank used oat seedlings as experimental material. [8] Therefore the blue/red peak height ratio of 1.5 in Frank [7] should be disregarded. [7] This conclusion was later shown to be erroneous.…”

“…In 1946, Frank used oat seedlings as experimental material. [7] Because the equipment available at the time necessitated exposure times of several hours, secondary processes interfered with the primary conversion process, and the internal shielding of blue light by carotenoids was not thought to be important. [7] This conclusion was later shown to be erroneous.…”