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Perlakuan awal adalah perlakuan sebelum penaburan untuk menambah kecepatan dan keseragaman perkecambahan benih yang ditabur di persemaian, lapangan atau untuk pengujian. Perlakuan awal semata-mata mempercepat proses alami pemecahan dormansi.
Dormansi fisik disebabkan oleh kulit buah yang keras dan impermeable atau penutup buah yang menghalangi imbibisi dan pertukaran gas. Fenomena ini sering disebut sebagai benih keras, istilah yang biasanya digunakan untuk benih leguminosae yang kedap air. Dormansi tipe ini adalah yang paling banyak ditemukan didaerah tropis. Karena struktur buahnya, sifat dormansi fisik untuk semua jenis sama dan perlukuan awal yang sama dapat diberikan. Tetapi karena perbedaan anatomi antara kulit biji atau pericarp, maka sifat dari perlakuan awal mungkin berbeda. Bebagai macam metode telah dikembangkan untuk mengatasi tipe dormansi ini, semua metode menggunakan perinsip yang sama yakni melubangi biji sedemikian rupa sehingga air dapat masuk dan penyerapan dapat berlangsung.
Perlakuan awal terhadap berbagai jenis harus disesuaikan dengan tingkat dormansi fisik.
a. Skarifikasi
Skarifikasi manual kulit biji melalui penusukan, pengoresan, pemecahan, pengikiran atau pembakaran, dengan bantuan pisau, jarum, kikir, kertas gosok, atau lainnya adalah cara yang paling efektif untuk mengatasi dormansi fisik. Karena setiap benih ditangani secara manual, dapat diberikan perlakuan individu sesuai dengan ketebalan biji. Pada hakekatnya semua benih dibuat permeabel dengan resiko kerusakan yang kecil, asal daerah radikel tidak rusak.
Seluruh permukaan kulit biji dapat dijadikan titik penyerapan air. Pada benih legum, lapisan sel palisade dari kulit biji menyerap air dan proses pelunakan menyebar dari titik ini keseluruh permukan kulit biji dalam beberapa jam. Pada saat yang sama embrio menyerap air. Skarifikasi manual efektif pada seluruh permukaan kulit biji, tetapi daerah microphylar dimana terdapat radicle, harus dihindari. Kerusakan pada daerah ini dapat merusak benih, sedangkan kerusakan pada kotiledon tidak akan mempengaruhi perkecambahan (Kremer, 1990).
b. Air Panas
Air panas mematahkan dormansi fisik pada leguminosae melalui teganganyang menyebabkan pecahnya lapisan macrosclereids (Brant et. al, 1971). Metode ini paling efektif bila benih direndam dengan air panas. Pencelupan sesaat juga lebih baik untuk mencegah kerusakan pada embrio karena bila perendaman paling lama, panas yang diteruskan kedalam embrio sehingga dapat menyebabkan kerusakan. Suhu tinggi dapat merusak benih dengan kulit tipis, jadi kepekaan terhadap suhu berfariasi tiap jenis. Umumnya benih kering yang masak atau kulit bijinya relatif tebal toleran terhadap perendaman sesaat dalam air mendidih.
Percobaan pada Casia siamea di Thailand, menunjukkan bahwa perendaman selama (1 sd 2) menit dalam air hangat 85oC atau perendaman pada suhu air 85°C yang diikuti dengan pendinginan selama (12 sd 36) jam menghasilkan persen kecambah antara (82 sd 89) persen, sedangkan perendaman lebih lama pada suhu 85°C sedikit menurunkan persen kecambah. Untuk jenis ini perendaman sesaat pada suhu yang tinggi atau perendaman pada suhu 85oC dalam waktu yang lebih lama dapat menyebabkan kerusakan (Kombo and Hellum, 1984 dalam Schmidt 2002).
c. Perlakuan dengan Larutan Asam
Larutan asam untuk perlakuan ini adalah asam sulfat pekat (H2SO4) asam ini menyebabkan kerusakan pada kulit biji dan dapat diterapkan pada legum maupun non legum. Tetapi metode ini tidak sesuai untuk benih yang mudah sekali menjadi permeable, karena asam akan merusak embrio. Lamanya perlakuan larutan asam harus memperhatikan 2 hal, yaitu:
1). kulit biji atau pericarp yang dapat diretakkan untuk memungkinkan imbibisi.
2). larutan asam tidak mengenai embrio.
Pada Casia siamea, (Kombo and Hellum, 1984 dalam Schmidt 2002) menemukan bahwa perendaman selama (15 sd 45) menit dalam larutan asam sulfat pekat (95 persen), menghasilkan perkecambahan 98 persen sedangkan perendaman (1 sd 10) menit terlalu cepat untuk mematahkan dormansi, sedangkan perendaman selama 60 menit atau lebih dapat menyebabkan kerusakan.
Perlakuan asam pada Enterolobiom cyclocarpum selama 15 menit terbukti efektif, sedangkan lebih lama (20 sd 25) menit memberikan hasil yang kurang baik (Barahman, 1996). Suginingsih, 1989 meneliti pengaruh perlakuan awal terhadap perkecambahan benih Aleurites moluccana Willd, dari hasil penelitian ini diperoleh hasil bahwa perendaman dengan larutan asam (H2SO4 ) selama 10 menit dengan konsentrasi 25 persen adalah yang paling baik dengan menghasilkan perkecambahan sebesar 76 persen sedangkan perendaman dengan konsentrasi 75 persen sama sekali benih tidak tumbuh.
Photosynthesis is the process by which plants make food. The word photosynthesis means putting together with light. In green plants, sunlight captured by chlorophyll enables carbon dioxide from the air to unite with water and minerals from the soil and create food. This process also releases oxygen into the air. People and animals must have this oxygen to breathe. Most photosynthesis takes place in small bodies called chloroplasts within the cells of plant leaves. These chloroplasts contain chlorophyll, which absorbs sunlight. Energy from the sun splits water molecules into hydrogen and oxygen. The hydrogen joins with carbon from the carbon dioxide to produce sugar. The sugar helps a plant make the fat, protein, starch, vitamins, and other materials that it needs to survive. See PHOTOSYNTHESIS. Some plants, called parasites and saprophytes, have little or no chlorophyll and cannot produce their own food through photosynthesis. These plants must rely on outside sources for food. Parasites attach to living plants and take the nutrients they need from these plants. Saprophytes grow on dead and decaying organisms, or use organic substances produced by living organisms for food. Mistletoe and dodder are common parasites found in many parts of the world. Mistletoe grows on the trunks and branches of many trees. It is called a partial parasite because it also makes some of its own food. Indian pipe is a saprophyte that grows near fungi. It uses organic materials produced by fungi for food. A plant called giant rafflesia is a parasite that grows on the roots and stems of other plants. It bears the largest flower of any known plant. Rafflesia flowers may grow over 3 feet (91 centimeters) wide. Respiration breaks down food and releases energy for a plant. The plant uses the energy for growth, reproduction, and repair. Respiration involves the breakdown of sugar. Some of the products resulting from this breakdown combine with oxygen, releasing carbon dioxide, energy, and water. Unlike photosynthesis, which takes place only during daylight, respiration goes on day and night throughout the life of a plant. Respiration increases rapidly with the spring growth of buds and leaves, and it decreases as winter approaches. Factors affecting plant growth. A plant's growth is shaped by both its heredity and its environment. A plant's heredity, for example, determines such characteristics as a flower's color and general size. These hereditary factors are passed on from generation to generation. Environmental factors include sunlight, climate, and soil condition. Hereditary factors. Within the nucleus of all plant cells are tiny bodies called chromosomes that contain hereditary units called genes. These bodies contain "instructions" that direct the growth of the plant. As the cells divide and multiply, the "instructions" are passed on to each new cell. See CELL; HEREDITY. Substances made within a plant also play a part in regulating plant growth. These substances, called hormones, control such activities as the growing of roots and the production of flowers and fruit. Botanists do not know exactly how all plant hormones work. But they have learned that certain hormones, called auxins, affect the growth of buds, leaves, roots, and stems. Other growth hormones, called gibberellins, make plants grow larger, cause blossoming, and speed seed germination. Still other hormones called cytokinins make plant cells divide. Environmental factors. All plants need light, a suitable climate, and an ample supply of water and minerals from the soil. But some species grow best in the sun, and others thrive in the shade. Plants also differ in the amount of water they require and in the temperatures they can survive. Such environmental factors affect the rate of growth, the size, and the reproduction of all plants. The growth of plants also is affected by the length of the periods of light and dark they receive. Some plants, including lettuce and spinach, bloom only when the photoperiod (period of daylight) is long. Such plants are called long-day plants. On the other hand, asters, chrysanthemums, and poinsettias are short-day plants. They bloom only when the dark period is long. Still other plants, among them marigolds and tomatoes, are not affected by the length of the photoperiod. They are called day-neutral plants. Plants also are affected in other ways by their environment. For example, a plant may display a bending movement called a tropism. In a tropism, an outside stimulus (force) causes a plant to bend in one direction. A plant may have either a positive or a negative tropism, depending on whether the plant bends toward or away from the stimulus. Tropisms are named according to the stimuli that cause them. Phototropism is bending caused by light, geotropism is caused by gravity, and hydrotropism is caused by water. A plant placed in a window exhibits positive phototropism when its stems and leaves grow toward the source of light. Roots, on the other hand, display negative phototropism and grow away from light. However, roots demonstrate positive geotropism. Even if a seed or bulb is planted upside down, its roots grow downward-toward the source of gravity. The stem of the same bulb shows negative geotropism by growing upward-away from the source of gravity. Hydrotropism occurs chiefly in roots and is almost always positive. See TROPISM. Some plants are affected by being touched. When the sensitive plant, Mimosa pudica, is touched, its leaflets quickly fold and its branches fall against its stem. A change in pressure within certain cells of the plant causes this action. After the stimulus has been removed, the plant's branches and leaflets return to their original position.
