NOPAL: CHARACTERISTICS, REPRODUCTION, NUTRITION, PROPERTIES - BIOLOGY - 2025

The nopal (Opuntia) is a genus of cactus whose species have been used for more than 100 years by the inhabitants of Mexico, the United States-Mexico border, and the United States. These cacti are also known as tunas, and they are plants for ornamental use.

Opuntia is the most diverse and widely distributed genus in America. In the world, about 1600 species are known. This genus is strongly associated with pollination by bees and coevolved with at least two genera of these insects.

Nopal with fruits. XHUANX

Spectacular examples of associations formed by these cacti known as nopaleras can be seen in nature. The nopaleras consist of the grouping in nature of cacti of various genera. Within these groupings there may be around 144 variants of the genus Opuntia.

The flowers and fruits of the Nopal are closely associated with pollination and seed dispersal by animals. Sexual reproduction and vegetative multiplication by fragmentation is common and explains the reproductive success of the genus Opuntia.

This cactus has been studied for its hypoglycemic properties, and its potential use for the treatment of type 2 diabetes.

Origin of the nopal

Mexico is the most important center of diversity with 669 species and 244 sub species of Opuntia. In fact, the Nopal is part of the figures that appear on its flag.

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Specifically, the genus Opuntia is native to central Mexico, and from there it has been dispersed into North America, Central America, and the Caribbean, and possibly South America in pre-Columbian times. From there, tourists have transported the Nopal from Mexico or nearby countries to Europe and the rest of the world.

characteristics

Estate

The roots of cacti in general receive little attention. They develop when the areolas make contact with the ground. These types of roots differ from other plants because they develop xeromorphic characteristics that allow the plant to survive in drought conditions. These roots can contribute to drought tolerance in different ways:

1. Restriction of the root surface and the decrease of its permeability to water, while the fine roots are covered with a layer more or less impermeable to water, or also have a layer of healing to avoid the loss of water in the dry soil.
2. Rapid absorption of the small amount of water supplied by light rains, through the formation of "rain roots" that develop a few hours after receiving the drops of water, and which disappear when the soil dries.
3. Decreased transpiration in the stems due to the high water potential of the roots.

Cladodio (stem)

The cladodes are the modified stems with leaf function. These stems have small shoots known as areoles that have hairs and thorns. The cladodes are succulent stems with green bark and photosynthetic function. They are oblong, spatula-oblong in shape, about 30 to 40 cm long, sometimes up to 80 cm, and 18-25 cm wide.

The areoles present in the cladodes produce, in addition to spines, small short spines like hairs called glochids. The stomata are abundant and are present on the entire surface of the stems and are evenly distributed.

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The epidermis of the cladodes has several functions such as regulating the movement of carbon dioxide into the plant as oxygen out of the plant, retaining water within the plant body, and protecting the plant from fungi, insects and light. intense solar.

Cactaceae have CAM metabolism (crassulaceae acid metabolism), and are generally considered drought resistant because they store large amounts of water in their stems.

Thorns

Consequently, the presence of thorns is a particular characteristic of cacti. The spines grow from the areoles and two types of spines can be distinguished (spines and hairs, the latter better known as glochids).

The spines are leaves modified to avoid the loss of water and serve as defense against predators. They are of great importance as a morphological character with taxonomic potential.

Flowers and flower buds

Unlike other cacti, in the nopal, the new cladodes (nopalitos) and flower buds grow from the areolar meristems. These can already produce a flower or a cactus. Once produced, the meristem does not carry out this process again.

Also, the phytohormone gibberellic acid has been studied to promote the development of flower buds and indole-butyric acid stimulates the vegetative growth of the buds. In this way, a high floral production reduces the production of nopalitos, and vice versa. The production of flowers and nopalitos can vary from one year to another throughout the life of the nopal.

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In subtropical regions, Opuntia flower buds begin when the monthly average temperature exceeds 16 ° C. This is in March-April in the Northern Hemisphere, and September-October in the Southern Hemisphere. The floral period fluctuates between 3 and 5 weeks in some species such as O. ficus-indica, and up to 25 weeks in O. joconostle.

Floral morphology

The floral axis shows from its base upwards, a pedicel that joins the flower with the cladode, as well as the pericarp that surrounds the lower ovary and the receptacle that contains the perianth, androecium and gynoecium. Some species have 24 tepals (O. polyacantha), and others have 19 (O. phaeacantha)

Opuntia flowers are generally yellow, but are also found in orange, pink, purple, red, white, or speckled. Hermaphroditic flowers are the most common. Also, they possess numerous stamens, for example, 265 in O. polyacantha, 358 in O. phaeacantha, 450 in O. viridirubra and 598 in O. brunneogemmia. These stamens are normally yellow or green with a circle or spiral in style.

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Pollen grains are spherical, cubic, or dodecahedral, 65-130 μm in diameter, and pointed or cross-linked.

Some species have nectaries at the base of the style. The style is simple, hollow, usually green or yellow, although sometimes it is pink, red, or orange. The stigma appears above the anthers and in the center of the flower. Each seminal primordium consists of the nucela, the embryo sac, the integuments, and the micropyle.

Fruit

Opuntia fruits are unilocular and polyspermic. There are three types of fruits: fleshy (they contain seeds with pulp around and a thin shell), dried fruits (seeds with almost no pulp and a thin shell), and xoconostle fruits (seeds with little pulp and a thick, acid shell).

In fleshy fruits, when these mature the skin thickens, the tubers become imperceptible due to the turgor of the tissue, and the surface becomes colored. 90% of the pulp is made up of parenchymal cells originating in the dorsal part of the epidermis of the funicular covering, and the remaining 10% is funicular tissue.

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In O. ficus-indica, the unripe green peel has stomatal and photosynthetic activity, contributing 8 to 10% to fruit growth. The areolas of fruits always have glochids and may have thorns or hairs, which may be from the flower stage.

Seeds

The growth and maturation of the seeds occurs 30 to 70 days after anthesis. Opuntia seed is small and ovoid or lens-shaped. An average seed can be 0.45 cm long, 0.35 wide, and 0.16 cm thick.

Prickly pear seeds show dormancy, which is associated with the impermeability of the integument and funicular hardening.

Taxonomy

The genus Opuntia was described by Miller in the year 1754, as follows:

- Kingdom: Plantae.

- Superphylum: Embryophyta.

- Phylum Tracheophyta.

- Class: Spermatopsida.

- Order: Caryophyllales.

- Family: Cactaceae.

- Subfamily: Opuntioideae.

- Genre: Opuntia P. Miller (1754).

Reproduction

Sexual reproduction

The fruit and vegetative parts, such as the spiny cladodes, are closely related to the dispersal of their seeds and the high and efficient vegetative dissemination by animals.

Vegetative multiplication appears to be more efficient than sexual reproduction. However, both reproductions (vegetative and sexual) possibly have contributed to the ecology and evolutionary success of this genus.

Anthesis

The reproductive biology of the fleshy fruit Opuntia species is related to anthesis. In this sense, flower development requires 21 to 47 days, and can be extended to 75 days.

In the northern hemisphere, anthesis occurs between May and July, and in the southern hemisphere it occurs between February and August. In nopales, flowering usually lasts between 6 and 12 hours, and if it starts late, it is completed the next day.

Regarding the reproduction of the Nopal, the bee-flower syndrome has been described. From there it is known that the floral structure has facilitated pollination by these insects, thus being the position of the style that protrudes from the stamens, and a large size of the nectary.

In this sense, the stigma lobes and the stigma itself are sticky and also facilitate the attachment of other insects, which serve as dispersers for pollen.

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With regard to the flowers, there is no evidence of the fragrance of Opuntia; however, more than 17 volatile compounds related to its aroma have been determined in O. ficus-indica fruits.

Pollinators

Visitors to Opuntia flowers are varied, the most abundant group being the Hymenopterans (84 species, and 19 identified only up to the genus), followed by Coleoptera (11 species, 11 genera), two Lepidopteran species and up to 10 species of birds..

These figures may increase according to the databases of the investigations that have been carried out, in addition to the fact that Opuntia pollinators have been determined only for a part of the species of this genus (approximately 19).

For its part, the species of bees that visit Opuntia vary during the flowering period. For example, in the highlands of San Luis de Potosí and Zacatecas they include continuous and abundant species, continuous and scarce species, rare species present for a short time at the end of the season, and casual species.

Characteristics of these insects

Thus, for a visiting insect to become an Opuntia pollinator it is required that:

1. That the insect is a consumer of pollen and nectar, and that at least 50% of the pollen it carries is Opuntial.
2. It must descend on the stigma.
3. The time you spend on the flower should be relatively short.
4. It must fly from flower to flower.
5. Measuring approximately 1.4 cm long.

Additionally, apomixis occurs frequently in Opuntia. Apomixis is the production of seeds without prior fertilization. In this plant genus, the development of adventitious embryos from the nucellar tissue is very common.

Vegetative multiplication

This type of reproduction occurs frequently in Opuntia. In fact, some species reproduce mainly in this way (O. fragilis, O. polyacantha, O. strigil and O. trichophora).

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Some studies have evaluated the importance of reproduction and multiplication in population growth. The high frequency of vegetative multiplication can preserve certain genetic characteristics.

Nutrition

Opuntioid cacti are cultivable species in arid zones, particularly due to their high efficiency in converting water into biomass. For this reason, they are recognized as an ideal crop for arid regimes.

Successfully domesticated crops such as O. ficus-indica play a fundamental role in the economy. Prickly pears are highly commercialized worldwide. That is why the cultivation of Nopal is as important as the cultivation of agave is for tequila in the agricultural economy of Mexico.

The opuntia cactus achieves high productivity, but only with proper fertilization. Average fertilization is 0.9% N, 0.16% P, 2.58% K, and 2.35% Ca, for an annual productivity of 20 tons per hectare per year, considering other macros and micronutrients.

Prickly pears are used as forage food, and as a supplement in animal nutrition.

Medicinal properties

The Nopal has medicinal properties derived from its fruits and cladodes. These cacti are an important source of bioactive substances and chemical constituents that increase the value of the cactus as a product.

Cacti have high antioxidant activity, they have vitamin C, flavonoids and betalains. In addition, several studies indicate that both the fruits and the cladodes have a high level of nutrients, minerals and vitamins.

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Recent studies show the potential of the Opuntia cactus to inhibit carcinogenesis in in vitro and in vivo cell line cultures.

In general, the Nopal has a medicinal function in the treatment of ulcers, anti-obesity, anti-inflammatory, healing, antiviral, cholesterol reduction, anti-cancer, neuroprotective, and hypoglycemia.

Representative species

The most representative species of Opuntia is O. ficus-indica. In addition to it, there is another that has been studied quite a lot such as: O. basilaris, O. chlorotica, O. fragilis, O. macrocentra, O. stricta, O. polyacantha, O. phaeacantha, O. aciculata, O. azurea and O lindheimeri.

References

1. Griffith, MP 2004. The origins of an important cactus crop, Opuntia Ficus-indica (Cactaceae): New molecular evidence. American Journal of Botany 91 (11): 1915-1921.
2. AO. 2017. Crop ecology, cultivation and uses of cactus pear. 224 p.
3. Reyes-Agüero, JA, Aguirre, JR, Valiente-Banuet, A. 2005. Reproductive biology of Opuntia: A review. Journal of Arid Environments 64: 549-585.
4. The Taxonomicon (2004-2019). Taxon: Genus Opuntia P. Miller (1754). Taken from: taxonomicon.taxonomy.nl
5. Aruwa, Ch., Amoo, S., Kudanga, T. 2018. Opuntia (Cactaceae) plant compounds, biological activities and prospects- A comprehensive review. Food Research International 112: 328-344.