Chlorophyll – the presence and absence of the green behind


our industry By Daniel Robarts, Horticulturist When talking to friends or family, many of


us working in environmental horticulture have surely claimed to be part of the “Green Industry.” While it can be generally stated that the business is comprised of a variety of interconnected businesses involved in production, distribution and services associated with ornamental plants, this collective may also conjure lofty (and often deserved!), “green” thoughts of conservation, environmental sustainability, and even carbon sequestration. But simply speaking, the title follows obvious fact that plants are generally green.


Tis color is due to the dominance of green pigments, the chlorophylls, present in plant tissues that absorb sunlight and transform it into chemical energy. Tis harnessed energy, combined with a stiff drink of water and a few deep breaths of carbon dioxide, is whipped up into the sugary mojo necessary for plants to perform activities such as growth, flowering, seed set. Basically, these pigments perform as big, green machines to cook up the hardy meals plants need to flourish. Tere are also secondary, “accessory pigments,”


carotenoids and anthocyanins, which also absorb light, but are typically masked by chlorophylls and occur in lesser concentrations. Tese pigments represent the non-green plant coloration. Tese have often have other roles including protection against UV damage and chemical stresses within the plant tissues and also promote pollination and seed dispersal by advertising gaudy flowers and subsequent, colorful, seed-filled fruits. Combined, these two groups of colorful molecules create the palette of greens and other colors in the leafed inhabitants of the landscape. Tough chlorophyll is really the literal namesake of the industry, and provides the meat and potatoes for a plant’s growth, vigor, and output, in many cases its absence often leads to plants greater horticultural interest. Due to random mutation, there are some plants that have varying levels of chlorophyll in their leaves and stems. Foliar variants may include purple or gold-leaved forms


GrowingMEGreen Coastal Maine Botanical Gardens


of typically green plants, where the chlorophyll may be scaled down or accessory pigments scaled up. Forms with bi- or tri-colored foliage occur as well, which are called variegated. Tis class of botanical freaks irregularly occurs in nature, and when discovered they are often prized horticultural treasure. Because of their lower capacity to produce energy, these plants are often less vigorous than their solid green counterparts. In some cases, the lower capacity to redirect the energy of the sun’s rays in such tissues may lead to increased susceptibility to sun scald. In some genera, variegation is commonplace and widely exploited


by breeders, such as hosta. For many plants, the likelihood of chance discovery of a variegated mutant is increased via tissue culture (a propagation method dominated by herbaceous taxa), due to the protocol employed or simply the sheer numbers of individuals produced. Due to difficult production or maturation times, variants in many woody genera are often less common, such as variegated oaks. Plants make an amazing variety of pigment molecules to mediate the light under which they grow. But have they green, gold, or flashing unruly, multicolored streaks, they all rely on a sturdy chlorophyll backbone to crank out the sugars for sustenance. And while we all can be proud in our green slogan, and all of its environmental and philosophical contributions and connotations, it’s important to remember the biology of the leafy products we grow, sell, and tend, similarly defines who we are.


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Photos by Rodney Eason of Coastal Maine Botanical Gardens


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