- Andrew Turnbull
Turfgrass stress - what is it and what can we do to help?
WHAT DO WE MEAN BY "PLANT STRESS"?
Most turfgrass managers and operatives understand the concept of ‘plant stress’, such as when under drought, heat, freezing and disease conditions, but not many understand what is happening inside the plant that affects its growth and health. This article introduces the subject of Reactive Oxygen Species (ROS), how the plant attempts to scavenge ROS with antioxidants, and how turfgrass managers can help to protect and enhance the plant's physiology and ability to manage stress levels..
Reactive Oxygen Species (ROS) are products of normal aerobic metabolism produced in the chloroplast, mitochondria and peroxisomes, and refer to any oxygen derivative that is more reactive than an oxygen molecule. ROS include hydrogen peroxide (H2O2), superoxide radical (O2×--), hydroxyl radical (OH×) and singlet oxygen (1O2). ROS are triggered by the plant in response to abiotic and biotic stress and can have a serious impact on plant metabolism through phytotoxicity during extended periods of plant stress.
ROS are formed during normal plant metabolism by the leakage of electrons onto O2 from the electron transport activities of chloroplasts, mitochondria, and plasma membranes, or as a
by-product of various metabolic pathways localized in different cellular compartments. Effects include lipid peroxidation, degradation of antioxidants
and initiation of gene expression.
Figure 1. Various causes responsible for the generation of ROS. Adapted from:
ROS production is restricted by ROS scavenging pathways and is a common event during all types of abiotic stress, regardless of the plant species. When the level of ROS exceeds the defense mechanisms, a cell is said to be in a state of “oxidative stress.” The delicate
balance between ROS generation and ROS scavenging is altered by stress factors
such as salinity, drought, extreme temperatures, heavy metals, pollution, high irradiance, pathogen infection, etc (Figure 1).
TYPES OF ROS
There are four main types of Reactive Oxygen Species, namely, singlet oxygen (1O2), hydrogen peroxide (H2O2), superoxide radical (O2•−), and hydroxyl radical (OH•) (Table 1).
Table 1. Different members of the ROS family and their attributes.
TARGETS OF ROS
Enhanced level of ROS can cause damage to biomolecules such as lipids (structural
components of cell membranes), proteins and DNA (Figure 2). These reactions can
alter intrinsic membrane properties like fluidity, ion transport, loss of enzyme activity,
protein cross-linking, inhibition of protein synthesis, DNA damage, and so forth
ultimately resulting in cell death.
Figure 2. Various targets of ROS. Adapted from; https://www.frontiersin.org/files/Articles/121942/fenvs-02-00053-r2/image_m/fenvs-02-00053-g003.jpg
ROS DEFENSE MACHINERY
Plant tolerance to stress-induced oxidative damage largely depends on rapid and efficient detoxification of ROS. Plants possess complex antioxidative defence systems comprising of non-enzymatic and enzymatic components that scavenge ROS (Table 2). In plant cells, specific ROS producing and scavenging systems are found in different organelles such as chloroplasts, mitochondria, and peroxisomes. Plants respond to ROS by collaboratively using one or more antioxidants at the same time, and a lot of energy is spent by the plant in defending itself. Because of this demand for energy (carbohydrates), plants can suffer as they put energy into protection at the expense of growth, such as recovery from wear. MorVita PURE helps to increase photosynthesis, enhance antioxidant activity, increase energy reserves and protect cell components from ROS attack.
Table 2. List of enzymatic and non-enzymatic antioxidants along with their functions and cellular localization. Adapted from:
MANAGING REACTIVE OXYGEN SPECIES
Protection of turfgrass surfaces from environmental and pathogen attack starts with providing the right rootzone conditions, water, balanced nutrients and light. Turfgrass surfaces grow best when mowing heights and frequencies are not too short, and operations such as thatch control, aeration, topdressing are carried out at the correct time and stage of growth, i.e. there are no short cuts to good turfgrass management. When these are in the right place other treatmetns can be considered.
Micronutrients (or trace elements) are directly or indirectly involved in many physiological and biochemical processes. Low levels of micronutrients allow an increase in ROS during stress conditions, but adequate levels increase the antioxidant activities by improving metabolism and decreasing harmful phenolic compounds, which enhances photosynthesis and reduces cell damage.
A low plant carbohydrate content reduces ability of plants to build new tissue, even if there are planty of nutrients. Carbohydrates are equivelent of fuel in the tank. No fuel, no growth.
Amino acids fulfil a wide variety of functions including the building blocks of proteins and are involved as active catalysts and precursors in all metabolic, regulatory and physiological aspects of plant metabolism. Under optimal conditions, proteins are able to perform the normal physiological functions but intensively manicured turfgrass surfaces, such as golf courses and sports pitches, are rarely operating under optimal conditions due to stress caused by low mowing heights and traffic. The application of L-Amino Acids plays an extremely important part in developing the proteins specifically designed to help chloroplasts, thylakoid membranes and photosystem machinery to function properly in stress conditions. L-Amino Acids have been shown to scavenge hydroxyl radicals by increasing superoxide dismutase (SOD), an important antioxidant enzyme, and help plants to withstand
stress due to temperature, drought, heavy metals, and in lawns low mowing heights, machinery & foot traffic.
Humic & Fulvic acids
Humic and fluvic acids are distinguished by their molecular size and activity in soils and plants, with humic acids having a larger molecular size than fulvic acids. Humic acids stimulate root initiation due to their auxin-like activity and ability to inhibit indoleacetic acid oxidase breakdown. Humic/fulvic acids contain antioxidant properties that promote the scavenging of free radicals (ROS), increase the availability of micronutrients and phosphate and potassium to the plant, and enhance the chlorophyll content in leaves.
Maintaining high levels of ascorbic acid (vitamin C) is essential for the scavenging of ROS, being an excellent scavenger of the hydroxyl radical that damages photosynthesis. Other antioxidants include a-tocopherol (vitamin E), carotenoids (B-carotene), vitamin B6 (found in Marmite) and mannitol (a sugar found in seaweed), which play a vital role in scavenging free radicals and help to protect chloroplasts, thylakoid membranes inside the chloroplasts, and photosynthetic machinery.
MorVita PURE supplies
All the micronutrients required for healthy and vibrant growth
Carbohydrates from cane sugar that supply the energy for growth
2.5% (w/w) L-amino acids that helps the plant to withstand environmental stress
Humic and fulvic acids that helps the plant to optimise the supplied nutrients
Vitamins that help the plant to recover from environmental and physical stress