(Special mode of nutrition in higher plants)
Autotrophic nature is the characteristics feature of plants except fungi, where self nourishment occurs by manufacturing their own food by photosynthesis, and completely independent.
On the other hand, some are of heterotrophic nature that depend upon others completely or partly for their nutrition. Such plants are unable to prepare their own food and nourish themselves. They obtain their food from various sources, either living or dead organisms in form of organic matter called as parasites and saprophytes respectively.
Out of them, some are symbionts and some are insectivorous also.
These plants grow upon living plants and absorb prepared food from their hosts by haustoria. It may be partial parasite (semi-parasite) or total parasite, which remain confind to the root as root parasite or to the stem, as stem parasite.
(a). TOTAL STEM PARASITES :-
Parasites completely depends on stem for food. eg- Cuscuta reflexa
(b). PARTIAL STEM PARASITES :-
The green plants, that are not entirely dependent on host plants,but grow partially and derive nutrients. eg- Viscum album(Mistletoe), Loranthus, Cassytha filiformis (Amarbeli), Arcenthobium.
(c). TOTAL ROOT PARASITES :-
The parasite completely depends on root of the higher plants for food. eg- Orbanche indica (Broomrape) as parasites on the roots of potato, tomato, brinjal, mustard, tobacco etc. Aeginetia indica as parasites on the roots of grasses and other plants. Balanophora dioica – parasitic on roots of forrest trees, Rafflesia arnoldi- parasitic on Vitis roots(not found in India, common in Java and Sumatra), Sapria himalayana – parasitic on roots of various plants.
(d). PARTIAL ROOT PARASITES :-
The parasite partially depends on the root of other plants. eg- Santalum album (Sandal wood), Striga, Pedicularis.
The plants that grow on dead organisms or decayed organic substances and draw their nutrition from them are SAPROPHYTES.
The fungi and some bacteria are common examples of SAPROPHYTES but some flowering plants are also included in such a group.
The common saprophytic flowering plants are – Monotropa (Indian pipe), Neottia (Bird’s nest orchids), Pholidota (Chain orchid) etc.
Some Orchids as Corallorhiza trifida (Coral-root), Epipogon, Sarcodes sanguinea (Snow plants or Snow ball), and Burmannia etc.
Two different Organisms live together, and both the partners get benifited by mutual help to each other, called symbionts, and such a relationship between the two is called as symbiosis.
The typical example is Lichen. Excluding it some higher plants also show symbiosis. They are –
- Mycorrhiza – Mycorrhiza are also a common example of symbiosis, where fungus is associated with the roots of higher plants.
The Mycorrhiza is of two types –
- Ectotrophic – when the fungus is external and attached with the surface of roots forming a fungal mantle in Oak (Querecus sp.),Brich (Betula sp), Beech and some conifers (Pines).
- Endotrophic – In this type, the fungi get associated internally to the cortical cell of root.
These fungi associated with roots, help in the absorption of water, mineral salts And nitrogenons organic substances from the soil as well as fixation of free nitrogen of atmosphere – eg. Many Orchids.
- Plants with root nodules – Formation of root nodules by Bacterium Rhizobium leguminosarum in the root of leguminous plants is also an example of symbiosis. Such bacteria grow symbiotically and fix elemental nitrogen of the atmosphere and make it available to the plant in form of nitrogenous compounds, while bacteria food and shelter from leguminous plant.
This is a true case of symbiosis.
- INSECTIVOROUS PLANTS
The insectivorous Plants are partly autotrophic as well as partly heterotrophic and usually grow in nitrogen deficient soil.
The insectivorous plants being green, prepare their own food by photosynthesis as autotrophs, but for fulfillment of their nitrogen deficiency, such plants feed upon insects or small animals for nitrogenous compounds from their bodies.
On the basis of mode trapping of insects, insectivorous plants may be divided into four categories:-
- Plants with modified leaves into sensitive glandular hairs on their surface, secrete a sweet, viscid, glistening sticky liquid. eg- Drosera (sundew), Pinguicula (Butterwort), Drosophyllum.
- Plants with modified leaves into sensitive hairs, called as trigger hairs found at their surface. eg- Dionaea(Venus’ fly trap), (Water fly-trap – rootless aquatic plants).
- The leaves modified into Pitchers. In Nepenthes (pitcher plant), only lamina is modified into pitcher, while in Sarracenia, Darlingtonia, Cephalotus and heliamphora, entire leaf gets modified into pitcher.
- The submerged aquatic root – less plats which have segmented leaves modified into small bladders. eg- Utricularia (Bladder wort).
- Drosera:- commonly called as Sundew are small insectivorous herbs whose leaves have glandular hairs at their upper surface, called as tentacles.
The glands of tentacles secrete a sticky purple juice which glitters in the sun like a dew drop, hence the name ‘Sundew’.
The insects are attracted towards the dew drops and the tentacles curve due to thigmonasty and the insect becomes trapped. The trapped insects are later digested by digestive enzymes (Pepsin hydrochloric acid) and amino acids (Proteins) are absorbed by the plant.
- Pinguicula:- commonly called as Butterwort, found in the alpine Himalayas (3000-4000m) is small herb. The leaves are arranged in rosette form, while surface is covered with numerous stalked and sessile glandular hairs.
These hairs secrete sticky mucilage as well as enzymes. The insects get stuck in the sticky substances, and simultaneously the margins of leaf roll inwardly and the insects get trapped.
The trapped insects are digested by secreting enzymes (Pepsin hydrochloric acid) and products are absorbed and assimilated by plant.
- Dioneaea:- commonly called as “ Venus’ fly trap”, a small herb which commonly grows in damp, mossy places.
The radical, and rosette leaves get modified into a rat trap like structure, which petiole becomes winged and the margin of lamina is deeply notched with incurved pointed teeth. Each half of the leaf blade is provided with three long pointed sensitive trigger hairs which helps in the sudden closing of lamina lobes after thingmonasty.
The trapped insect is digested by the action of digestive enzymes Pepsin hydrochloric acid secreted from glands and proteinous matter is absorbed by the plant.
- Aldrovanda:- commonly called as “water fly trap” is a root less sub- merged or free floating aquatic plant found in salty lakes or salty marshes.
It is similar to Dionaea but in Aldrovanda there are several hairs along the sides of the mid rib with some bristeles. The margins of leaf are modified into minute inwardly curved teeth.
Numerous digestive glands are found at the upper surface of the leaf that contains digestive enzymes which digest the trapped water insects.
- Pitcher plant:- Entire leaf or a part of is modified into peculiar pitcher like structure which acts as insect- catching trap.
In Nepenthes, the lamina is modified into a pitcher of 10 to 20cm or more in length with a lid which is a modified leaf apex. The pitcher is supported by tendrillar stalk (modified petiole) and green laminated modified leafbase, performing the function of leaf.
In Sarracenia, Darlingionia,Cephalotus etc, whole leaf is modified into sessile pitcher forming a rosette. The Pitcher consists of numerous smooth hairs pointed downwardly and has numerous digestive glands at the inner surface. The pitcher is partly filled with fluid, and contains digestive enzymes (trypsin / Pepsin hydrochlorides). The trapped insects are digested and their proteinous substances are absorbed by the plant.
- Utricularia:- commonly called as Bladder wort is a root less submerged floating aquatic herb. The leaves are greatly dissected and segmented, where some segments are modified into small bladders (03-05mm in diameter).
The bladder consists of trap door and branched hairs or bristles. Numerous digestive glands filled with enzymes are found at the inner surface of the bladder. The small aquatic animals are trapped along with fluid by the help of trapping door, and are digested by digestive enzymes and digestive products are absorbed by the plants.
Dr. Amrendra Kumar
Institute:- Science student’s circle
MIG/42, opposite BATA, Near
Shalimar Sweets, Kankarbagh,
patna-20. (M):- 7061412121.