Transportasi Air, Nutrisi, dan Unsur Hara

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Transportasi Air, Nutrisi,

dan Unsur Hara

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Source dan Sink

• Source: bagian di mana fotosintat memulai

proses transportasi (tempat produksi atau menyimpan)

• Sink: tempat di mana fotosintat di tempatkan (bagian yang

membutuhkan maupun penyimpanan)

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Xylem

• Jaringan xylem memindahkan air dan unsur yang terkandung di

dalamnya dari akar ke daun.

• Saluran xylem

tersusun atas sel-sel mati.

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Phloem

• Jaringan floem

memindahkan fotosintat dari tempat produksi ke tempat yang

membutuhkan atau penyimpanan.

• Jaringan floem tersusun atas sel-sel hidup dan berdampingan dengan sel-sel pendamping

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Transportasi air terjadi di 3

bagian

• Transpirasi adalah proses pemindahan air

dan mineral dari akar menuju daun dan

kemudian dilepaskan ke udara dalam

bentuk uap. Proses ini melibatkan 3

langkah dasar :

• Penyerapan di rambut akar.

• Aktifitas kapiler di jaringan floem.

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Bagian1: Perakaran

• Akar menyerap air dan mineral melalui 4

proses:

• Transport aktif mineral ke dalam rambut

akar

• Difusi ke dalam perisikel

• Transport aktif ke dalam silinder vaskuler

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Pita Kaspari

• Pita kaspari mengontrol jumlah air yang masuk ke dalam jaringan

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Step 2: Gaya Kapiler

• Kohesi: molekul air cenderung

berinteraksi satu sama lain melalui ikatan hidrogen

• Adhesi: molekul air cenderung untuk menempel pada permukaan benda yang dilalui

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Gaya Kapiler

• Gaya kohesi dan

adhesi

menyebabkan air dapat merambat

melalui kolom yang sangat sempit.

• Semakin sempit

kolom, semakin tinggi air akan merambat.

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Tekanan Air di Perakaran

• Transpirasi menyebabkan perbedaan tekanan yang

dapat menarik air dari akar dan sampai batang.

• Tekanan air rendah di akar sehingga menarik lebih banyak air.

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Part 3: Penguapan

• Penguapan pada permukaan daun memicu pergerakan

air di xylem.

• Penguapan adalah pemicu proses transpirasi yang terkuat

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Stomata control

• Sel penjaga di stomata sangat sensitif terhadap cahaya, CO₂, dan penguapan. • Stomata membuka

saat cahaya dan

CO₂ pada tingkatan yang rendah, dan

akan menutup saat terjadi defisiensi air k

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Stomata

• Ketika stomata terbuka, penguapan

menarik air dari daun. Pertukaran gas

juga dapat terjadi untuk menjaga

berlangsungnya proses fotosintesis.

• Ketika stomata tertutup, penguapan tidak

dan pertukaran gas tidak terjadi,

sehingga fotosintesis dan transpirasi

melambat.

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Getah

• Getah terdiri dari gula dilarutkan dalam

air pada konsentrasi tinggi: biasanya

antara 10% dan 25%.

• Karena ini sangat terkonsentrasi,

tanaman harus menggunakan

transportasi aktif untuk melawan gradien

difusi sebagai bagian dari proses

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Pressure-flow theory

• Pergerakan gula dimulai dari sumber dan

dipompa ke dalam sel tabung floem

• Osmosis memicu pergerakan air ke

dalam sel-sel dan meningkatkan

tekanan.

• Tekanan kemudian memicu pergerakan

getah getah

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Pressure flow 1

• Daun merupakan

sumber gula

• Glukosa dan fruktosa

disintesis melalui proses fotosintesis untuk

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Pressure-flow 2

• transpor aktif

digunakan untuk

memuat sukrosa ke dalam tabung floem terhadap gradien

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Pressure-flow 3

• Konsentrasi tinggi sukrosa dalam sel floem menyebabkan pergerakan air oleh osmosis

• Fenomena ini

meningkatkan tekanan dan menyebabkan

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Pressure-flow 4

• Buah merupakan contoh

dari jaringan sink

• Sukrosa secara aktif

diangkut keluar dari floem ke dalam sel buah.

• Di akar, sukrosa diubah menjadi pati

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Pressure-flow 5

• Saat konsentrasi gula di dalam sel tabung floem menurun, air bergerak keluar dari tabung melalui proses osmosis.

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Pressure-flow 6

• Saat air bergerak keluar oleh osmosis, tekanan dalam sel tabung

saringan turun.

• Perbedaan tekanan sepanjang kolom sel menyebabkan getah terus mengalir.

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CHAPTER XII

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Air

• 90% dari total masa tanaman disusun

oleh air. Fungsi air

1. Diperlukan dalam proses perkecambahan. 2. Sebagai bagian dari struktur tanaman

3. Pembawa mineral ke dalam tanaman

4. Memindahkan fotosintat dan produk biokimia ke seluruh tanaman

5. Mendinginkan suhu tanaman melalui evaporasi 6. Terlibat dalam proses fotosintesis.

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Karakter air:

Fenomena polaritas air

mengakibatkan gaya tarik menarik antara molekul air. Air juga dapat

menarik/ditarik oleh

• Kation, seperti Na+, K+, and Ca++, or

• Anion atau koloid tanah liat di tanah

•Merupakan pelarut umum (universal solvent) • salah satu unsur alami yang paling stabil

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Air Tanah

Ketersediaan

Walaupun air ada dalam tanah, bukan berarti bahwa air tersedia bagi tanaman

Pori-pori tanah terisi oleh air, udara, atau gabungan keduanya.

– Saat ruang pori terisi air, tanah akan menjadi jenuh. Kondisi tanah yang jenuh tidak bagus untuk tanaman karena oksigen yang diperlukan untuk respirasi tidak ada.

– Saat ruang pori banyak diisi udara, tanah menjadi kering.

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• The number and size of the soil pores vary with the soil's texture and structure.

• Clay soils have smaller but more

numerous pores than

sandy soils. Thus, an

equal volume of clay soil holds more water than a sandy soil

when the pores are filled (Fig. 12-2).

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• The ability of the soil to retain water is called its water-holding capacity. Fig. 12-3.

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Water Movement and Retention in Soil

Three forces are responsible for water movement within the soil.

1- Gravity causes water to move downward and is the

principal force when a soil is saturated = percolation.

2- Adhesion is the force of attraction between unlike

molecules (soil particles and water).

3- Cohesion is the force of attraction between like

molecules (water and water).

• 2+ 3 = capillary motion

• The latter two forces can cause water to move by capillarity in any direction—upward,

downward, or laterally—and are the principal forces that move water in an unsaturated soil.

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• The upward movement of water, called capillary

rise, is responsible for the loss of water from the soil surface by evaporation (Fig. 12-4).

• As soil dries, the water film surrounding each soil particle thins.

Consequently, the

adhesive and cohesive forces of attraction

increase rapidly, making it more difficult for the

plant to extract water that is held tightly in soil

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• Salts are present in soil water. The salts create

osmotic energy, and if the salts are present in a

sufficiently high concentration, the osmotic energy prevents water movement into the plant (Fig. 12-6)

= Plasmolysis.

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• After a prolonged rain or irrigation, the air in the soil pores is displaced with water. In this

condition, the soil is saturated,

• When no more water is added, losses continue, first from the larger macropores=percolation and then from the smaller micropores=infiltration.

Loss of water continues until the adhesive and

cohesive forces equal gravity.

• At this moisture content, the soil is said to be at

field capacity. The water has drained from the

macropores but the micropores still contain water.

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• If no water is added, eventually the soil reaches a moisture content that does not sustain plant life and the plants permanently wilt.

• The soil moisture content at which a plant wilts and cannot recover when placed in an

environment of 100 percent relative humidity is termed the permanent wilting point (PWP).

• Soil texture determines the relationship between soil water content and soil moisture tension (Fig. 12-8).

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Available water (AW) is defined as the soil moisture between field

capacity (FC) and the permanent wilting point (PWP): AW = FC - PWP

Water between FC and saturation is not considered available because it is lost through drainage.

Water at tensions greater than PWP is held too tightly by the soil for plants to remove.

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PLANT WATER

Absorption and Conduction of Water

The energy to move the water comes from the water potential gradient that develops in the soil, plant, and air continuum:

– In most cases, the water potential of moist soils is greater than that of the roots, so water flows into the roots (some anatomical

features of the root aid or deter this process).

– Once inside the xylem of the root, however, the flow of water is

almost strictly pressure

dependent, with the pressure decreasing from the root to the stem, to the leaves, to the air (Fig. 12-10).

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• The upward movement of water and dissolved minerals occur mainly in the xylem. The xylem extends from the root through the stem and

other parts of the plant.

• The upward movement is sometimes called the

transpiration stream because transpiration is

the primary cause of this movement.

• The upward transpiration pull in the leaves is started by the evaporation of water molecules from the outer surfaces of the mesophyll cells.

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• Most of the water is lost from the leaves by

transpiration.

• Water loss in the plant is regulated to a certain extent by the opening and closing of stomata on the leaf

surfaces.

• Not all water leaves the leaf:

1. Some water is part of the plant's structures or held in the cytoplasm.

2. Some is used for biochemical processes, 3. Some is stored in the tonoplast.

• The pressure of water inside a cell creates turgor

pressure, which gives plants rigidity. When there is

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Absorption and Transport of Mineral Nutrients

The sap in root cells has concentrations 500 to 10,000

times higher than those of the same element in the soil solution.

– If simple diffusion were the only mechanism involved in taking up soil nutrients, the mineral nutrients could not move into the roots against such a high concentration gradient.

– In addition, the plasma membranes of cells are largely impermeable to the movement of ions.

• Energy is required to move ions

– Against the concentration gradient and – Through the impermeable membranes.

• This energy is obtained from the respiration of starches and sugars that originated in the photosynthetic

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Translocation of Sugars

• Sugars that are synthesized during

photosynthesis move throughout the plant,

primarily in the phloem tissues.

• The movement is

– Mostly downward from leaves to roots, – Lateral or even upward movement from

leaves to fruits or buds or other storage organs.

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In woody perennials,

when phloem tissue is severed by girdling:

1. The tissue above the cut proliferates =رثاكتت 2. The tissue below the cut is starved يناعت= for

photosynthates (Fig. 12-12). This can severely stunt and even kill a tree

The rate of translocation of sugars in the phloem is, in some instances, more than a thousand

times faster than simple diffusion of sugar through water.

The forces that create these high rates of movement are called active transport.