Abstract

Frost is an important abiotic stress for plants and crops because of the economic losses that are incurred. Plants have two mechanisms for freezing protection: freezing avoidance and freezing tolerance. The former prevents extrinsic and/or intrinsic ice nucleation, while the latter provides plants with tools to survive apoplastic ice formation, by several coordinated physiological and biochemical features such as the increase in cryoprotectants (metabolites and proteins) which in general maintain cell membrane and cells macromolecules stability, cause a freezing point depression or decrease the cell osmolarity preventing the severe cell dehydration caused by apoplastic freezing. Many products against freezing have been developed, and there are at least 20 products on the international market. Ten products mainly avoid ice formation by forming semi-permeable or permeable membranes that inhibit extrinsic ice nucleation over leaves, three products work for favouring tolerating ice formation in plants, and two use both mechanisms of action. Some kind of lipids, such as phospholipids and alpha-tocopherol, effectively maintain the stability and integrity of cell membranes, while some osmolytes (mainly polyols) decrease the freezing point of water, both inside and outside the cell, but also can interact with the polar moieties of phospholipids stabilizing membranes. Despite this, more information on products for crop protection against freezing is required in order to determine their effectiveness. New formulations that protect crops against freezing must include ingredients that employ both mechanisms. The use of lipids is likely to continue while new alternatives that reduce ice formation are evaluated, among which antifreeze and cryoprotective proteins may offer attractive alternatives.