Generally, fleshy fruits can be divided into two groups based on the presence or absence of a respiratory increase at the onset of ripening. This respiratory increase—which is preceded, or accompanied, by a rise in ethylene—is called a climacteric, and there are marked differences in the development of climacteric and non-climacteric fruits. Climacteric fruit can be either monocots or dicots and the ripening of these fruits can still be achieved even if the fruit has been harvested at the end of their growth period (prior to ripening on the parent plant). Non-climacteric fruits ripen without ethylene and respiration bursts, the ripening process is slower, and for the most part they will not be able to ripen if the fruit is not attached to the parent plant. Examples of climacteric fruits include

apples An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...

bananas A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", distinguis ...

melons A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". Th ...

apricots An apricot (, ) is a fruit, or the tree that bears the fruit, of several species in the genus '' Prunus''. Usually, an apricot is from the species '' P. armeniaca'', but the fruits of the other species in ''Prunus'' sect. ''Armeniaca'' are al ...

tomatoes The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

, as well as most stone fruits. Non-climacteric fruits on the other hand include

citrus fruits ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is nativ ...

grapes A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years ago ...

, and

strawberries The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...

(However, non-climacteric melons and apricots do exist, and grapes and strawberries harbor several active ethylene receptors.) Essentially, a key difference between climacteric and non-climacteric fruits (particularly for commercial production) is that climacteric fruits continue to ripen following their harvest, whereas non-climacteric fruits do not. The accumulation of starch over the early stages of climacteric fruit development may be a key issue, as starch can be converted to sugars after harvest.

Overview

The climacteric is a stage of

fruit ripening Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make the ...

associated with increased

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...

production and a rise in

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

and is the final physiological process that marks the end of fruit maturation and the beginning of fruit

senescence Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...

. Its defining point is a sudden rise in respiration of the fruit, and normally takes place without any external influences. After the climacteric period, respiration rates (noted by

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

production) return to or dip below the pre-climacteric rates. The climacteric event also leads to other changes in the fruit, including

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

changes and

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

release. For those fruits raised as

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...

, the climacteric event marks the peak of edible ripeness, with fruits having the best taste and texture for consumption. After the event, fruits are more susceptible to

fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

invasion and begin to degrade by

cell death Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as d ...

. If a fruit were to over-ripen, it could be detrimental to the post harvest of the fruit, meaning the shipment and storage of the fruits for marketing. The over ripening could also lead to a pathogen attack, which can lead to the fruits developing diseases and exhibiting symptoms like necrosis and leaf wilting.

Ethylene Production

Ethylene is a hormone in plants known for its role in accelerating the ripening of fleshy fruits. There are two systems, depending on the stage of development, for ethylene production in climacteric fruit. The first system occurs in immature climacteric fruit, where ethylene will inhibit the biosynthesis of more ethylene by a negative feedback system. This ensures that the fruit doesn't begin to undergo ripening until it is fully mature. The second system for ethylene production acts in mature climacteric fruit. In this autocatalytic system, the ethylene will promote its own biosynthesis and will make sure that the fruit will ripen evenly after the ripening begins. In other words, a small amount of ethylene in mature, climacteric fruits, will cause a burst of ethylene production and induce even ripening. Ethylene production begins when 1-aminocyclopropane-1-carboxylic acid (the precursor of ethylene) is formed from the amino acid methionine (Met). An adenosynlated step takes place to change Met to SAM. SAM is then metabolized to ACC by 5ʹ-methylthioadenosine by ACC synthase which is then recycled back into 1-methylcyclopropane (1-MCP, an ethylene inhibitor) where another round of ethylene biosynthesis takes place. Along with the production and control of ethylene, auxin also plays a major role in climacteric fruit ripening. Auxin, a plant hormone that allows for cell elongation, is accumulated during the initial growing and developmental phases of the plants life cycle. During ethylene gene induction it was found that auxin related genes (aux/IAA and AUX1) represents the transcription factors that induce 1-MCP. Ripening includes many changes in fleshy fruit including changes in color, texture, and firmness. Additionally, there may be an increase in certain volatiles (metabolites the plant releases into the air) as well as changes in sugar (starch, sucrose, glucose, fructose, etc.) and acid (malic, citric, and ascorbic) balance. These changes, particularly in sugars, are important in determining fruit quality and sweetness.

References

{{DEFAULTSORT:Climacteric (Botany) Fruit Plant physiology