Detecting a Botanical SOS

David Hanson photo

Life isn't always a walk in the park for houseplants. You've got to make do with crummy artificial light and you must rely on often-clueless humans for water and fertilizer. If they overdo it, or if they forget to water you at all, you're probably a goner, at which point they toss you out and buy a new plant to torture.

But even well-meaning humans can't always tell if they are over- or under-watering that philodendron in the kitchen. Wouldn't it be nice if your plants could tell you when they need a drink? Well, now they can, thanks to UNM Assistant Professor David Hanson and his student Chris Erickson. They've developed an easy, low-cost way to determine when plants are water stressed even before they start to show it.

First, we need to know a little about how green plants produce sugar via photosynthesis. When chlorophyll a absorbs sunlight, electrons in the chlorophyll gain energy or become “excited.” This gain in energy ultimately is used to produce a form of chemical energy that the plant can use to power the synthesis of sugars and other biological molecules. The excited electrons lost by chlorophyll a are replaced by electrons from water.

Erickson and Hanson reasoned that without enough water, photosynthesis wouldn't proceed efficiently, and they came up with a simple way to measure such efficiency: they simply take a leaf sample and determine how sensitive the chlorophyll a in the plant cells is to light. They determine such sensitivity by measuring the degree to which the chlorophyll fluoresces following light exposure with a hand-held device called a “flurometer.”

To test their idea, they grew Dracaena deremensis, a common houseplant, under both optimal and water-stressed conditions. They found that they could detect water stress using chlorophyll a fluorescence long before outward signs of trouble, such as wilting or dying leaves, appeared. In other words, anyone with a flurometer can check a plant's health at any time, allowing conscientious plant owners or plant maintenance personnel to provide optimum watering—a simple way to make sure your green housemates stay in the pink.